redmancr:Valencia being left out isn't because he's not good enough, it's because he's an out and out winger which means he only fits a formation with either a block of 4 or a block of 5. 4231 needs attacking midfielders, and 433 needs wide forwards.
If last year is anything to go by, Fergie will have a block of 3 interchanging attackers towards the middle and left hand side, Welbeck LW & SS (with the possibility of Cleverley or more attacking of the two coming in as well) and leaving a large place on the right hand side where Valencia will patrol. I don't see Fergie deviating from that very much.

Average positions in one of last years games. Pretty much all the games followed this pattern.