I hope Ole has tightened the defence. I wouldn't mind a 0-0 draw at Old Trafford and 0-1 away win 
Times have changed; and if i consider injuries to both Manchester United and AC Milan core players; it would be surprising if AC Milan escape old trafford with a nnil nil. Manchester United is winning tonight with more than 3 goals; Manchester United 4 - 0 AC Milan
A 4-0 result seem to me as an exaggeration for this match.
Milan will feel especially Ibrahimovic's absence in this match but I don't think they will lose this match with a too many goal difference. I feel confident about Milan will also score but Man Utd will defeat them 2-1 or 3-1, in my opinion.