If Ospreys are to win this one, the first thing they must do is find a way of stopping Zach Mercer.
The Gloucester back-row has carried far more times - 78 - than any other player in the competition this season.
Williams back in front of the Shed
Gloucester v Ospreys (20:00 BST)
Huw Evans Picture Agency and Getty ImagesCopyright: Huw Evans Picture Agency and Getty Images
Owen Williams has actually scored more points for Gloucester than his current team Ospreys.
It is almost four years since the Wales fly-half left Kingsholm following a three-year stint that yielded 121 points in 44 appearances.
He headed down the road to Worcester before returning to Wales to join Ospreys in 2022 where he has now succeeded Gloucester-bound Gareth Anscombe in the number 10 jersey.
Will he get a warm welcome back from the Shed?
Quarter-final 'huge' for Gloucester - May
Gloucester v Ospreys (20:00 BST)
Rex FeaturesCopyright: Rex Features
Gloucester winger Jonny May said this quarter-final against Ospreys is a "huge" chance to show what the team "believe we can do".
The Cherry and Whites have the home advantage when they face the Welsh side tonight.
Gloucester beat French club Castres to reach the knockout stages last week, with May one of the try-scorers.
"It's huge for us, it's huge for this group," May told BBC Radio Gloucestershire.
"A lot of hard work has gone into this group the last few years and maybe we haven't got the rewards that we would have hoped for and deserved, given the fact we really have put in the hard graft.
"There's been some challenging times this season as well but to be in a quarter-final feels awesome.
"It feels like we're getting an opportunity to play in a huge game and getting to show what we can do and what we believe we can do."
'There's something about Friday night's at Kingsholm'
There has been plenty of doom and gloom around Welsh rugby this season following drastic cost-cutting among the regions and a Wooden Spoon for the national team in the Six Nations.
But Ospreys have been the one glimmer of hope.
They are the only Welsh side in the United Rugby Championship play-off places and are the last survivors in Europe.
"We are excited we are flying the flag for Wales," said head coach Toby Booth.
"We want to be a team people can get around, and instead of all the gloom around Welsh rugby, there is something to celebrate.
"There is a massive mutual support and empathy for Welsh rugby within each region.
"You get good luck messages and support each other because ultimately we want to do well, because in the big picture it's good we will all benefit from.
"Let's get behind something, even if it's for a moment. If other sides were in a similar position, I'd be supportive and wish them well.
"Because if we have a successful campaign, more players want to play rugby and be involved. It can only be good for the health of the game."
Cup kings Gloucester
Gloucester v Ospreys (20:00 BST)
Getty ImagesCopyright: Getty Images
Gloucester may be struggling in the league but are proving the cup kings this season.
The Cherry & Whites have won 12 from 12 ties so far, including their Premiership Cup triumph over Leicester Tigers last month.
“The more knock out rugby we play the better," director of rugby George Skivington said.
"It’s hard work to get to the latter stages of any competition and to have these knock out games at Kingsholm is even more exciting.
“But we’ve got to stay focussed on what’s in front of us and that’s a tough Ospreys team. We’ll have to be at our best."
He added ahead of this intriguing Anglo-Welsh clash: “We’re very close so I expect there’ll be some travelling support and this place will be bouncing.
"Europe is always exciting because you play opposition that you don’t always play.”
Skivington knows Ospreys will arrive with plenty of confidence after an impressive win over Sale Sharks last weekend.
He said “They’re in the quarter-finals for a reason, they’re a good team and we’re in for a tough game.
“The focus for us is on ourselves, as it should be. But we watched the Ospreys game against Sale and we know there’s a physical hard working team coming.”
Ospreys hooker Sam Parry has been passed fit for tonight's European Challenge Cup quarter-final.
Parry missed the 23-15 win against Sale with a hamstring problem but returns as Lewis Lloyd drops to the replacements' bench.
It is the only change to Toby Booth's starting side that includes Wales internationals Owen Watkin and Gareth Thomas.
British & Irish Lions flanker Justin Tipuric captains the side.
Ospreys are still without long-term injuries George North, Alex Cuthbert, Jac Morgan and Dewi Lake.
Ospreys: Jack Walsh; Luke Morgan, Keiran Williams, Owen Watkin, Keelan Giles; Owen Williams, Reuben Morgan-Williams; Gareth Thomas, Sam Parry, Tom Botha, James Ratti, Adam Beard, Harri Deaves, Justin Tipuric (capt), Morgan Morris.
Replacements: Lewis Lloyd, Nicky Smith, Rhys Henry, Huw Sutton, Morgan Morse, Luke Davies, Dan Edwards, Max Nagy.
Hastings back for Glos
Gloucester v Ospreys (20:00 BST)
Getty ImagesCopyright: Getty Images
Adam Hastings damaged his knee scoring against Castres in JanuaryImage caption: Adam Hastings damaged his knee scoring against Castres in January
Gloucester's Scotland fly-half Adam Hastings returns from injury, while Wales centre Max Llewellyn starts.
Hastings, who announced this week he will leave Gloucester at the end of the season and return to Glasgow, has been sidelined since January with a knee injury he picked up while scoring a try against Castres Olympique.
Director of rugby George Skivington said: “Hasto is in a good spot. We have got a little bit of competition at 10 now which is good for us.
"Charlie had a good game at the weekend and Santi had a good game against Leicester particularly and then George Barton helped us win the Prem Cup final."
Hastings returns to face former Gloucester fly-half Owen Williams and lines up alongside Italy scrum-half Stephen Varney.
But the Cherry & Whites are missing injured trio Val Rapava-Ruskin, Cameron Jordan and Ollie Thorley.
Gloucester: Santi Carreras; Jonny May, Max Llewellyn, Seb Atkinson, Jake Morris; Adam Hastings, Stephen Varney; Jamal Ford-Robinson, Seb Blake, Kirill Gotovtsev, Freddie Clarke, Freddie Thomas, Ruan Ackermann, Lewis Ludlow, (capt), Zach Mercer.
Replacements: Santi Socino, Mayco Vivas, Fraser Balmain, Albert Tuisue, Jack Clement, Caolan Engelfield, Charlie Atkinson, Chris Harris.
Good evening
Gloucester v Ospreys (20:00 BST)
Getty ImagesCopyright: Getty Images
Welcome to Kingsholm for what promises to be a fascinating night of EPCR Challenge Cup quarter-final rugby.
Ospreys arrive at Gloucester hoping to reach a European semi-final for the first time. The hosts aim to continue their unbeaten run in cup competitions this season.
Live Reporting
Gareth Griffiths
All times stated are UK
Stop Mercer!
Gloucester v Ospreys (20:00 BST)
If Ospreys are to win this one, the first thing they must do is find a way of stopping Zach Mercer.
The Gloucester back-row has carried far more times - 78 - than any other player in the competition this season.
Williams back in front of the Shed
Gloucester v Ospreys (20:00 BST)
Owen Williams has actually scored more points for Gloucester than his current team Ospreys.
It is almost four years since the Wales fly-half left Kingsholm following a three-year stint that yielded 121 points in 44 appearances.
He headed down the road to Worcester before returning to Wales to join Ospreys in 2022 where he has now succeeded Gloucester-bound Gareth Anscombe in the number 10 jersey.
Will he get a warm welcome back from the Shed?
Quarter-final 'huge' for Gloucester - May
Gloucester v Ospreys (20:00 BST)
Gloucester winger Jonny May said this quarter-final against Ospreys is a "huge" chance to show what the team "believe we can do".
The Cherry and Whites have the home advantage when they face the Welsh side tonight.
Gloucester beat French club Castres to reach the knockout stages last week, with May one of the try-scorers.
"It's huge for us, it's huge for this group," May told BBC Radio Gloucestershire.
"A lot of hard work has gone into this group the last few years and maybe we haven't got the rewards that we would have hoped for and deserved, given the fact we really have put in the hard graft.
"There's been some challenging times this season as well but to be in a quarter-final feels awesome.
"It feels like we're getting an opportunity to play in a huge game and getting to show what we can do and what we believe we can do."
'There's something about Friday night's at Kingsholm'
Gloucester v Ospreys (20:00 BST)
Ospreys flying the flag for Wales
Gloucester v Ospreys (20:00 BST)
There has been plenty of doom and gloom around Welsh rugby this season following drastic cost-cutting among the regions and a Wooden Spoon for the national team in the Six Nations.
But Ospreys have been the one glimmer of hope.
They are the only Welsh side in the United Rugby Championship play-off places and are the last survivors in Europe.
"We are excited we are flying the flag for Wales," said head coach Toby Booth.
"We want to be a team people can get around, and instead of all the gloom around Welsh rugby, there is something to celebrate.
"There is a massive mutual support and empathy for Welsh rugby within each region.
"You get good luck messages and support each other because ultimately we want to do well, because in the big picture it's good we will all benefit from.
"Let's get behind something, even if it's for a moment. If other sides were in a similar position, I'd be supportive and wish them well.
"Because if we have a successful campaign, more players want to play rugby and be involved. It can only be good for the health of the game."
Cup kings Gloucester
Gloucester v Ospreys (20:00 BST)
Gloucester may be struggling in the league but are proving the cup kings this season.
The Cherry & Whites have won 12 from 12 ties so far, including their Premiership Cup triumph over Leicester Tigers last month.
“The more knock out rugby we play the better," director of rugby George Skivington said.
"It’s hard work to get to the latter stages of any competition and to have these knock out games at Kingsholm is even more exciting.
“But we’ve got to stay focussed on what’s in front of us and that’s a tough Ospreys team. We’ll have to be at our best."
He added ahead of this intriguing Anglo-Welsh clash: “We’re very close so I expect there’ll be some travelling support and this place will be bouncing.
"Europe is always exciting because you play opposition that you don’t always play.”
Skivington knows Ospreys will arrive with plenty of confidence after an impressive win over Sale Sharks last weekend.
He said “They’re in the quarter-finals for a reason, they’re a good team and we’re in for a tough game.
“The focus for us is on ourselves, as it should be. But we watched the Ospreys game against Sale and we know there’s a physical hard working team coming.”
Parry fit for Ospreys
Gloucester v Ospreys (20:00 BST)
Ospreys hooker Sam Parry has been passed fit for tonight's European Challenge Cup quarter-final.
Parry missed the 23-15 win against Sale with a hamstring problem but returns as Lewis Lloyd drops to the replacements' bench.
It is the only change to Toby Booth's starting side that includes Wales internationals Owen Watkin and Gareth Thomas.
British & Irish Lions flanker Justin Tipuric captains the side.
Ospreys are still without long-term injuries George North, Alex Cuthbert, Jac Morgan and Dewi Lake.
Ospreys: Jack Walsh; Luke Morgan, Keiran Williams, Owen Watkin, Keelan Giles; Owen Williams, Reuben Morgan-Williams; Gareth Thomas, Sam Parry, Tom Botha, James Ratti, Adam Beard, Harri Deaves, Justin Tipuric (capt), Morgan Morris.
Replacements: Lewis Lloyd, Nicky Smith, Rhys Henry, Huw Sutton, Morgan Morse, Luke Davies, Dan Edwards, Max Nagy.
Hastings back for Glos
Gloucester v Ospreys (20:00 BST)
Gloucester's Scotland fly-half Adam Hastings returns from injury, while Wales centre Max Llewellyn starts.
Hastings, who announced this week he will leave Gloucester at the end of the season and return to Glasgow, has been sidelined since January with a knee injury he picked up while scoring a try against Castres Olympique.
Director of rugby George Skivington said: “Hasto is in a good spot. We have got a little bit of competition at 10 now which is good for us.
"Charlie had a good game at the weekend and Santi had a good game against Leicester particularly and then George Barton helped us win the Prem Cup final."
Hastings returns to face former Gloucester fly-half Owen Williams and lines up alongside Italy scrum-half Stephen Varney.
But the Cherry & Whites are missing injured trio Val Rapava-Ruskin, Cameron Jordan and Ollie Thorley.
Gloucester: Santi Carreras; Jonny May, Max Llewellyn, Seb Atkinson, Jake Morris; Adam Hastings, Stephen Varney; Jamal Ford-Robinson, Seb Blake, Kirill Gotovtsev, Freddie Clarke, Freddie Thomas, Ruan Ackermann, Lewis Ludlow, (capt), Zach Mercer.
Replacements: Santi Socino, Mayco Vivas, Fraser Balmain, Albert Tuisue, Jack Clement, Caolan Engelfield, Charlie Atkinson, Chris Harris.
Good evening
Gloucester v Ospreys (20:00 BST)
Welcome to Kingsholm for what promises to be a fascinating night of EPCR Challenge Cup quarter-final rugby.
Ospreys arrive at Gloucester hoping to reach a European semi-final for the first time. The hosts aim to continue their unbeaten run in cup competitions this season.
Something has to give.