Alessandro Florenzi has undergone surgery on his left knee and Milan have not given a timeframe for his recovery.
Florenzi is on a season-long loan at Milan from Roma, with the Rossoneri having the option to make the deal permanent.
The 31-year-old full-back has played 27 times this season for the Serie A leaders, though only 13 of those have been starts.
Florenzi suffered the injury in Monday’s goalless draw with Bologna at San Siro that saw Milan drop two points in the race for the Scudetto, though they remain a point ahead of second-placed Napoli.
A statement on the club website read: “AC Milan can confirm that Alessandro Florenzi today underwent an arthroscopic operation on his left knee, conducted by Dr Piero Paolo Mariani.
“The meniscectomy, undertaken with AC Milan club doctor Lucio Genesio in attendance, was successful. Alessandro will commence the rehabilitation process right away.”
Florenzi was in the Italy squad that won Euro 2020 last year and the group that failed to qualify for the 2022 World Cup after losing to North Macedonia in the play-offs.
Stefano Pioli’s side travel to Torino on Sunday.