Paulo Fonseca was left disappointed with Milan's lack of defensive responsibility in their shock 2-1 defeat to newly promoted Parma on Saturday. (More Football News)
Milan were stunned inside 83 seconds when Dennis Man gave the hosts a shock lead, only for Christian Pulisic to restore parity just after the hour-mark.
However, substitute Matteo Cancellieri struck in the closing exchanges to secure their first triumph over Milan in Serie A since 4-2 win back in March 2014.
It marked an early bump in Fonseca's tenure with the Rossoneri, acknowledging that his side must improve at the back to succeed this season.
"I'm disappointed. It's difficult to explain our defensive attitude. It's clear that we have a defensive problem," Fonseca told a press conference.
"For Parma it was too easy when they attacked. I'm not just talking to the defenders, I'm talking about the whole team, how they defend collectively and individually.
"I take responsibility for what the team does, but we have to recognise these defensive problems."
Milan created the better chances during the contest at Stadio Ennio Tardini, but only five of their 17 shots were on target, the same number as Parma managed from eight fewer attempts.
The visitors also underperformed their expected goals (xG) by 1.01, missing three big chances while also striking the woodwork in the encounter.
Of the 90 duels between the two sides, Parma had a success rate of 54.4% compared to Milan's 45.6%, with Fonseca left bemused by his sides underwhelming display.
"The team works well during the week, I think I see improvement in view of the match. Then today we arrive here and in the first situation we concede a goal," Fonseca added.
"We behaved badly defensively in all moments of the match. (There's) a problem to solve, of attitude. We need to work as a team.
"We lose the ball too easily. This allows a team that defends deep to create chances. We have made mistakes in preventive marking, defensive recoveries that we do not do together."
