A final reminder of what is needed for Arsenal and Chelsea to go through. First up, Arsenal:

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Meanwhile, if Chelsea avoid defeat, they are through.

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Ian Dennis
BBC Radio 5 live senior football reporter at Stamford Bridge

"I think tonight if Jose doesn't get the win his position will be extremely precarious. You cannot underestimate the significance of this game at Stamford Bridge."

Mark Lawrenson
Former Liverpool defender in Greece

"If Chelsea do go out of the Champions League this evening I really do think Jose Mourinho is under massive pressure because what will be left for Chelsea to go for this season."

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Chelsea manager Jose Mourinho, talking to BT Sport, says he has not contemplated the Blues failing to reach the last 16:

"Winning the group is the objective but if in the end we get a draw and qualify that is good.

"But we don't plan to start the game with that in mind - we want to win. We know winning is difficult, because this is not a group match now - this is knockout now."

On Diego Costa returning to his starting XI: "It's not about Costa, it's about the team. There is a clear contrast between our results and the atmosphere in the squad. I understand people have doubts, but the players want to win. I hope the contradiction ends tonight.

"But we need to put the ball in the net which we have not been doing."

A final reminder of the Chelsea team. Big night for Diego Costa, can he fire the Blues into the last 16 and ease the pressure on his manager?

Chelsea XI: Courtois; Ivanovic, Zouma, Terry, Azpilicueta; Ramires, Matic; Willian, Oscar, Hazard;Costa.

A tough day for Garry Monk - but it could end up being a very relaxing Christmas. 

We've been asking what doodles your manager would draw during a press conference. Send them over to #bbcfootball, external

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Arsenal manager Arsene Wenger, speaking to BT Sport: "We have to be brave - it will be hostile against a motivated team who are physically very strong. We need to be committed but disciplined and controlled.

"I gave Theo half an hour at the weekend. I don't think he has 90 minutes in his body at the moment but I decided to start him. It's risky, but we need to score goals tonight so it was needed.

"We need to produce a top, top, top performance because I think Olympiakos are an under-rated team."

Here's a reminder of how Arsenal will line up tonight. It will be interesting to see how far forward Theo Walcott will play, on his return to the side in place of The Ox.

Arsenal XI: Cech; Bellerin, Mertesacker, Koscielny, Monreal; Ramsey, Flamini; Ozil, Walcott, Campbell; Giroud.

Olympiakos: Roberto; Elabdellaoui, Da Costa, Siovas, Masuaku; Kasami, Milivojevic, Fortounis, Seba, Pardo; Ideye.

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Can Arsenal avoid a slip-up in Greece? They have failed to win there in each of their last five visits.

Mark Lawrenson
Former Liverpool defender in Greece

"It is very difficult for Arsenal. If they can get that first goal in the first 25 minutes it will change the opposition's thinking. It will change the dynamics. Suddenly you think 'we can do this'."

You can listen to Mark on BBC Radio 5 live now.

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Arsenal fans may not want to remember their brief European campaign 16 years ago - the last time they failed to reach the last 16 - but Manchester United supporters will be wishing they were partying like its 1999.

That was the year they staged one of the most memorable comebacks in football to win the Champions League, beating Bayern Munich 2-1.

Nothing memorable about this year's adventure as Louis van Gaal's side failed to reach the last 16 after losing 3-2 to Wolfsburg on Tuesday. 

All that money spent and they finished their most important game of the season so far with Jesse Lingard, Nick Powell and 18-year-old Cameron Borthwick-Jackson in their side. Madness.

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Phil Wye
BBC Radio 5 live in Athens

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"A walk up to the mighty Acropolis of Athens this morning yielded a chat with a few Arsenal fans.

"General consensus among them was optimism, that the Gunners won't get turned over tonight but that a two-goal or 3-2 win would be "a big ask." 

"Minus Sanchez, Cazorla & Coquelin in their ranks, it's hard to disagree.

"Olympiakos have a 100% domestic record this season and only Bayern Munich - in Champions League Group F - have toppled Greek football's number one team.

"But Arsene Wenger reminded us yesterday that his Arsenal teams "have a history of positive results" and suggested that Olympiakos have it all to lose.

"Can't help but think that for the Gunners to pull this off, a Mesut Ozil masterclass will be needed this evening."

Tough gig Kev, tough gig.

BBC Radio 5 Live

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Diego Costa is currently going through the pre-match warm-ups with the rest of the Chelsea squad. 

Would the Blues be better off without the striker? That's one of the questions Mark Chapman, Mark Lawrenson, John Murray and the Daily Mail's Neil Ashton are debating right now on BBC Radio 5 live.

What do you think? Diego's fault or - as Ashton wrote on Sunday - isMourinho losing a grip?, external

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Iker Casillas is in the Porto goal tonight. Could be an awkward encounter if he bumps into Jose Mourinho in the tunnel before kick off.

The two fell out when Mourinho was manager of Real Madrid, with Casillas dropped from the side.

No doubt he'll have a point to prove tonight.

Porto need a win at Stamford Bridge to top Group G - but the Portuguese runners-up have not named an adventurous side.

Five recognised defenders, two holding midfielders and no out-and-out striker.

A draw will be enough for Porto to finish as group winners, with Chelsea progressing as runners-up - unless Dynamo Kiev win and the Portuguese side are out. Confused? Here's why.

Porto XI: Casillas, Maxi Pereira, Martins Indi, Maicon, Marcano, Layún, Brahimi, Herrera, Danilo, Imbula, Corona.

Mark Lawrenson
Former Liverpool defender in Greece

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"I think it's great for Gary Neville. I don't know him fantastically but I think he will look at the players and give them a chance, regardless of who they are or who their agent is. 

"It's typical of us to all start saying 'he is the next Manchester United manager' or 'he is the next England manager'. He hasn't even managed a game yet, give the lad a chance."

John Bennett
BBC World Service in Valencia

"The fans I've been speaking to here at the Mestalla seem pretty excited about what Gary Neville can bring to the club.

"They're skeptical about his close links to the owner and his lack of management experience but seem delighted to have got rid of the previous coach.

"The supporters here have the reputation of being the hardest to please in Spain but - for now - Neville has their backing.

"Neville certainly won't let them down when it comes to hard work. I saw him arriving at the Mestalla today seven hours before kick-off."