Giacomo Bonaventura will be sidelined for up to nine months following an operation on his knee, AC Milan have confirmed.
The midfielder had surgery on an osteochondral lesion to his left knee in the United States on Tuesday.
Milan released a statement to confirm the procedure in Pittsburgh had been a success, but they do not expect him to play again this season.
The Rossoneri said on the club's official website: “AC Milan announces that Giacomo Bonaventura underwent surgery on the osteochondral lesion of his left knee.
“Today's cartilage repair procedure, carried out in Pittsburgh by the surgeons Volker Musahl and Freddie Fu in the presence of the AC Milan medical staff, was successful and the recovery time is estimated in 8/9 months.”
It was initially speculated the Italy international would only be out for up to five months.
The news is a blow to head coach Gennaro Gattuso, with Lucas Biglia battling a calf problem this season and Hakan Calhanoglu also struggling for full fitness.
Milan currently sit fifth in the Italian top-flight table, 15 points adrift of leaders Juventus.