England midfielder Ruben Loftus-Cheek was carried off on a stretcher with a head injury during AC Milan's 1-0 defeat by Parma.
He collided with Parma goalkeeper Edoardo Corvi when challenging for a cross early in the Serie A game at the San Siro on Sunday.
Loftus-Cheek's head and neck were put in a brace before he was taken off.
Sky Italia reported that he broke his jaw and several teeth.
A significant injury could affect Loftus-Cheek's chances of making England's squad for the World Cup, which starts in June.
He made his first England appearance in seven years when he came on as a substitute against Wales in October, having been recalled by manager Thomas Tuchel.
Milan are second in the table, 10 points behind rivals Inter Milan, who beat Lecce 2-0 on Saturday to claim their seventh successive league win.
Mariano Troilo scored the winner for Parma in the 80th minute to leave them 12th in the table.