The Red Devils came into this game on the back of a Derby win over Manchester City and they were full of confidence.
However, the home side were plagued with injuries and Ole Gunnar Solsjkaer was without several key players today.
The likes of Luke Shaw, Paul Pogba, Edinson Cavani and Marcus Rashford were all missing for the hosts.
Manchester United decided to field a relatively inexperienced attack with the likes of Mason Greenwood, Dan James and Amad Diallo.
AC Milan opened the scoring through Franck Kessie but the goal was ruled out in the first half due to handball. The Italian side will feel hard done by as the ball did not seem to hit the hand before it was volleyed in.
Manchester United had the best chance of the game on the 38th minute but Harry Maguire hit the post with an open goal staring down on him.
January signing Amad Diallo made his mark for Manchester United with the opening goal of the game five minutes into the second half but United failed to preserve their advantage and Simon Kjaer managed to grind out a vital draw for the away side with a goal on the 91st minute.
AC Milan will now fancy their chances of going through to the next round of the competition by winning at home in the next leg.
It will be interesting to see if the Manchester United players are back from injury in time for the second leg and they can inspire their side to turn this around.
He’s creative. He plays with freedom. A great pass by Bruno [Fernandes] by the way, that’s of course what makes the goal. Amad, he’s been on the pitch before, but nice goal. He’s got lots to learn and he’ll be better off from having that.Ole Solskjaer on Amad Dialo
Very disappointed to conceded with one of the last kicks of the ball, or head. That makes it harder of course, but it was always going to be going down to the second game there, anyway.
I’ve seen him [Henderson] save them, but it’s the structure that we lose. We dropped too deep and we get blocked off and they get the header on. We should have attacked the ball with the men we had there.
We were a bit too slow with the possesion. That’s the learning we have to get into ourselves, we have to perform every single week. We’re playing against good teams. Probably a draw is a fair result.Ole Solskjaer on conceding goal at added time