Who will Sir Alex Ferguson and Kenny Dalglish choose for this one-time knockout game against their rivals?
Liverpool's team is about the fittest it has ever been, and minus the suspension of Luis Suarez, they will not be missing any key players.
On the other hand, Sir Alex Ferguson has had to deal with injury after injury throughout the season and there is no exception in this game.
Liverpool will be looking to inch its way towards another cup final by the end of the game. Manchester United will be looking to ensure that they keep fighting on all fronts.
Some players on each team will have something to prove and others will want to continue making opponents sweat.
Johnny Evans has received his share of criticism this season but he put in a decent shift against Arsenal and will look to continue that tomorrow. Antonio Valencia will want to keep up his fine form
On the other end, Andy Carroll is one of the few Liverpool players yet to pick up his play while others around him have. Steven Gerrard has been very influential since his return from injury
Let's take a look at the possible lineups for each team.
Manchester United Formation: 4-4-2
Lindegaard; Rafael, Smalling, Evans, Evra; Valencia, Carrick, Giggs, Park; Rooney, Welbeck
Liverpool Formation: 4-4-2
Reina; Johnson, Skrtel, Agger, Enrique; Henderson, Gerrard, Adam, Downing; Bellamy, Carroll