Amad Diallo opened the scoring in Manchester, but a late Simon Kjaer header levelled things up and handed AC Milan the advantage going into the second tie.
There are some big name returns for this clash, with Paul Pogba and Zlatan Ibrahimovic both available again after injury.
When is AC Milan vs Manchester United?
The match kicks off at 8pm on Thursday 18 March at the San Siro.
AC Milan vs Manchester United TV channel and live stream
BT Sport 2 will be showing the game live with coverage starting at 7.15pm. Subscribers can stream the action on BT Sport Player or the BT Sport app.
Manchester United welcome back Paul Pogba and Donny van de Beek after injury, but Edinson Cavani, Anthony Martial, Eric Bailly and Juan Mata remain out.
The big news from AC Milan is that Zlatan Ibrahimovic is fit again after an abductor problem and will feature.
AC Milan vs Man Utd odds
5/2 AC Milan
23/20 Man Utd
Odds courtesy of Betfair
AC Milan vs Manchester United head-to-head in last five meetings
11 Mar 2021: Man Utd 1-1 AC Milan – Europa League
10 Mar 2010: Man Utd 4-0 AC Milan – Champions League
16 Feb 2010: AC Milan 2-3 Man Utd – Champions League
02 May 2007: AC Milan 3-0 Man Utd – Champions League
24 Apr 2007: Man Utd 3-2 AC Milan – Champions League