Young picked up a knock to his knee last weekend and was left out of England's squad for the upcoming World Cup qualifiers as a result. The boss has also insisted Wayne Rooney will only be out for four weeks despite press speculation he could be missing for twice that length of time after picking up a nasty-looking injury against Fulham.
"In terms of injuries, it was nice of the FA to let everyone know Ashley Young is injured," said Sir Alex. "He's out after the injury last week. It's not serious.
"Centre-back is our main concern at the moment. Jonny Evans played on Wednesday [against Tottenham at Under-21 level] and came through fine. He's the strongest option we've got.
"Phil Jones has done some training but isn't ready yet. Rio Ferdinand's in the same boat. At least we have one centre-back available, which is an improvement. It allows us to put Michael Carrick back in midfield.
"Wayne's out for four weeks. It's nothing serious on the actual gash - it's a bad one but it was treated carefully very quickly. We don't expect any complications from it. I think he'll be back in four weeks. The fact it's a gash and not a muscle or joint injury means he can do a lot of work in the gymnasium. We're not too bad with that."