Not only will United have to be at their very best in order to get past the Chelsea defence and also stop their attackers, they will HAVE to control the middle of the park if they want to get anything at all from the game.
This means that whoever Van Gaal picks as his midfield anchors will have to not only stop Matic from being able to break up the play, but also stop Cesc from being the one dictating the tempo of the game.