Juventus defender Giorgio Chiellini has torn a muscle in his left knee, the club announced on Monday.
Chiellini, 33, lasted just 11 minutes in Juve's 1-0 home loss to Napoli in the two sides' top-of-the-table clash in Turin on Sunday.
Tests performed the following day confirmed a tear of the biceps femoris muscle in his knee.
Chiellini has already begun therapy but no other details were provided by the club regarding the length of recovery.
With the loss, Juventus, who are seeking their seventh straight Serie A title, lead Maurizio Sarri's side by just one point with just four matches to play.
The Bianconeri will also face AC Milan in the Coppa Italia final on May 9.