Postpublished at 18:24 Greenwich Mean Time 23 January 2021
We'll hear from Alan Shearer and Micah Richards at half-time but in the meantime take a look at some highlights from the earlier games...
Use play icon to watch live coverage alongside commentary from Martin Fisher & Rachel Brown-Finnis
Also listen to commentary from BBC Radio 5 Live, BBC Radio Sheffield & BBC Radio Devon
Sheffield United are bottom of the Premier League; Plymouth are 11th in League One
Four-time winners Sheffield United last won the competition in 1925
Sheffield United beat Bristol Rovers in round three; Plymouth overcame Huddersfield
Emma Sanders, Phil Dawkes, Gary Rose, Tom Rostance and Shamoon Hafez
We'll hear from Alan Shearer and Micah Richards at half-time but in the meantime take a look at some highlights from the earlier games...
Cheltenham 0-0 Man City
Gary Lineker
Ex-England striker on BBC One
We saw some fireworks in the first half but the only rocket we might see is one from Pep Guardiola at half-time.
Cheltenham 0-0 Man City
And they do so successfully.
An excellent half from the Robins, holding firm against the Premier League giants.
Cheltenham 0-0 Man City
City still unable to make any inroads.
One more minute for Cheltenham to hold out.
Cheltenham 0-0 Man City
A booming long throw from Ben Tozer for the first time in the game and it causes allsorts of problems for Zac Steffen, who has to come through a raft of players to punch the ball away.
The American does the same from the resulting corner.
Excellent goalkeeping.
Cheltenham 0-0 Man City
Six minutes added on in the first half.
#bbcfootball or text to 81111 (UK only)
Adam Oldroyd: Nothing worse than someone who copies an idiot. If you're going to be an idiot, be original!
Thomas Sleet: Would the ref have brought the players off if it wasn’t Manchester City they were against
Cheltenham 0-0 Man City
Play has finally resumed.
There'll be a fair few minutes to be added on.
Cheltenham 0-0 Man City
Danny Murphy
Former Liverpool and England midfielder on BBC One
Michael Duff will be saying 'more of the same'. You can tell they work on their defence a lot, they are really disciplined.
I thought it would take a while for City to get going, and that's what has happened.
Cheltenham 0-0 Man City
We've had this before in the competition in Stockport's tie against West Ham.
The officials and players continue to have a chit chat on the touchline.
"Doing much tonight?"
"No mate, watching a bit of Casualty later, what else can you do!"
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At half time somebody needs to check the Cheltenham Town left back's pockets. That's where you'll find Riyad Mahrez.
Andrew in Clitheroe
Cheltenham 0-0 Man City
They're still going off so players have come to the side of the pitch to get a drink.
Can see some policemen striding by the side of the pitch.
What are they going to do???
Cheltenham 0-0 Man City
Referee Stuart Attwell has brought play to halt as fireworks are going off outside and landing on the pitch.
Cheltenham 0-0 Man City
Riyad Mahrez's long range, dipping drive is gathered at the second attempt by Robins goalkeeper Josh Griffiths.
Good save.
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Matt Andrews: Is there a sniper in Cheltenham? City players going down left right and centre and I can hear the screams in Warwickshire
Cheltenham 0-0 Man City
City have some space to work with for the first time, Riyad Mahrez bursting clear of the defence but his touch takes him wide.
By the time he retrieves it and gets a cross in, Charlie Raglan can head clear.
Poor from the Algerian.
Cheltenham 0-0 Man City
Danny Murphy
Former Liverpool and England midfielder on BBC One
There's a little bit of a lack on intensity about City's play. They have made a lot of changes, and lost a bit of rhythm.
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City fan. Creeping nerves. Lacking zip. Oozing complacency apart from Doyle and Foden.
Derek
Cheltenham 0-0 Man City
City skipper Fernandinho scored a cracker at Old Trafford in the League Cup but can't do the same this time, curling a strike which drifts wide of the post.
Think Josh Griffiths had it covered.
Cheltenham 0-0 Man City
Danny Murphy
Former Liverpool and England midfielder on BBC One
Phil Foden is starting to grow and get involved in the game more, he's been absolutely brilliant recently but he doesn't quite wrap his foot around the ball.