There are plenty of guessing games going on as to the personnel the manager will employ with some reports predicting Phil Jones will be given a man-marking job on Cristiano Ronaldo and others expecting Wayne Rooney to drop deep or Shinji Kagawa to be the key.
Sir Alex has added to the suspense by admitting: "There could also be a surprise from both teams. I'm trying to guess what they could do to blunt us and also what I can do to annoy them."
So how will the Reds 'annoy' Jose Mourinho's Spanish champions? Get in touch via Talking Reds or using the hashtag #manutdtactics on Twitter and we will post a selection of the best comments here. We would like your thoughts on the starting XI, formation and any specific tactics the boss could use to get the right result.
Alex91Gonzalez: Of course Rooney's best position (in my opinion at least) is as a striker. In this case though, I would have him in midfield just in front of Jones and Carrick. His ability to hold on the ball and create chances would be more important from him in this game as he's done that a lot this season every single time Sir Alex played him in a role like that.
David D'Genius: RVP should play as a lone striker, Rooney mandated to drift in from the left. No opponent should be man-marked, but watch Ronaldo.
Tudur 'Tate' Jones: I'm not a fan of man-marking and it's dangerous with Champions League refereeing. Offence is the best form of defence - defend with the ball.