However, the under-fire Celtic boss refused to be drawn into criticising his goalkeeper after another subpar showing from Vasilis Barkas.
The Scottish champions travelled to the Serie A leaders a beleaguered squad having lost their dominance over Scottish football’s major honours with Sunday’s 2-0 defeat to Ross County in the Betfred Cup.
With pressure mounting on Neil Lennon they needed a big performance against Milan and it looked for a while that’s exactly what would happen.
Goals from Tom Rogic and Odsonne Edouard had the visitors 2-0 up inside 14 minutes. But a free-kick from Hakan Calhanoglu and a quick second from Samu Castillejo soon tied up the scores.
Jens Petter Hauge put the hosts in front shortly after the restart before Brahim Diaz made sure of things later in the game, ensuring Celtic stay bottom of the group on one point, having already been eliminated following last week’s 4-1 defeat in Prague.
Despite it being another defeat, Lennon was positive in his reaction after the match. He also picked out a couple of individuals for praise.
He said: "We looked a good team tonight. Body language was good; attitude was good. We’ve got to look at the positives. I thought we looked good for a large part of the game. I don’t think I’ve ever been involved in a team that has gone 2-0 up at the San Siro.
"Edouard looked more like himself, Frimpong was outstanding. I thought [Scott] Brown had a good game as well.”
Further questions have been asked of Celtic’s goalkeeping situation after Barkas was found wanting for Calhanoglu’s free-kick. The Greek international gambled on the shot going over the wall, only to see it fly into the net in the area where he was supposed to cover.
The summer signing only recently returned to the side for Sunday’s match with County and Lennon refused to point the finger of blame in his direction.
He responded when asked about Barkas: "I’m not going to single out individuals. We’ll analyse it as a group and take it from there.”