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 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.Obviously 4-0 prediction for Man United is just an over confidence prediction or I can call it as an underestimation for Milan.
Both teams has similar injuries issue for their main players but I think Milan is a bit worst than United.
If Milan is able to minimize the creativity of Bruno Fernandes, I think Milan will be able to get better result than what is expected/predicted by most people.