Stefano Pioli ordered Milan to cut out "trivial mistakes" after a 2-2 draw at Lecce left the Rossoneri nine points behind runaway Serie A leaders Napoli.
Last season's champions trailed Lecce 2-0 after 23 minutes on Saturday, before Rafael Leao and Davide Calabria hauled them back to level terms.
An exciting final 20 minutes could have brought a winner for either team, yet there were to be no more goals, and while the point nudged Milan up to second place, that gap to Napoli will be difficult to overcome.
Head coach Pioli told DAZN: "In the first half, we missed everything we could possibly miss. We made unforced mistakes and the match became more difficult."
Theo Hernandez turned a cross from Federico Di Francesco into his own goal to give Lecce a third-minute lead, and Pioli said after the game: "We need to be more clear-headed."
Milan's haul of 38 points from 18 games points to a sturdy start to their title defence, with the caveat Napoli have made a roaring opening to the season and have won 15 of their opening 18 matches.
Pioli said: "We are in line with last season, but it is also true that in this phase we are getting much less than we would like. We can do better and avoid trivial mistakes.
"We have to recover our principles of play and do it continuously."
Leao has had a goal involvement in each of Milan's last four league games, the first time he has had such a run, and his season's total of 13 involvements (eight goals, five assists) in 17 appearances is five ahead of where he was after the same number of matches in 2021-22.
Pioli denied the approaching Supercoppa Italiana game against Inter was a distraction to Milan.
That trophy game is coming up on Wednesday, and Pioli said: "It's a straight match against a great opponent, so we'll do everything to be ready."
He hopes to have Ante Rebic available for that game in Riyadh after recent muscle injury trouble, and Zlatan Ibrahimovic could also be in line for a return before long, the Milan boss added.
Ibrahimovic has yet to play this season, having undergone knee surgery at the end of the Scudetto-winning campaign.