The manager has a real dilemma in terms of his personnel for the two huge fixtures this week as he bids to avoid a repeat of last season's defeat to Chelsea.
The weary Reds returned from a first-leg European defeat in Bavaria to meet the eventual champions at Old Trafford and suffered a crucial 2-1 lossfollowing Didier Drogba's controversial offside goal in 2010.
A similar result this time around would send the Londoners top of the table with two games to play so Sir Alex is fully aware of the need to have his players fresh and firing for the weekend as Carlo Ancelotti's team have their feet up after we dumped them out of Europe.
Circumstances are a little different this time around - United are in Manchester rather than abroad and the league clash kicks off on Sunday afternoon as opposed to Saturday lunchtime while a two-goal advantage over Schalke is already in the bag.
Nonetheless, this is a Champions League semi-final we are talking about and there is no way the boss will be complacent with a Wembley date against Barcelona within our grasp. So changes will be made for Wednesday's fixture but two victories will still be the name of the game.
So which two XIs will take to the field at Old Trafford this week? Such is the strength in depth, the manager could pick two completely different line-ups and still be confident of success. That won't happen but he's hinted at a number of changes on Wednesday with Dimitar Berbatov, Michael Owen and Paul Scholes all already forwarded as starters. Calling upon players of that calibre and with such experience on the big stage will surely stand the Reds in good stead. Wayne Rooney has a tight hamstring and Javier Hernandez looked tired at Arsenal so it's probably right that they sit this one out.
Sir Alex is keen to retain a familiar-looking defence but Rafael is literally a like-for-like