The African midfielder had to go under the knife to repair a torn anterior cruciate ligament and is expected to return to action only at the end of the year
The Ghana international has torn the anterior cruciate ligament in his left leg and was forced to go under the knife at the La Madonnina clinic in Milan on Tuesday.
A statement on the Italian club's website read: "Milan would like to announce that Sulley Muntari has undergone surgery for the reconstruction of the anterior cruciate ligament in his left knee.
"The recovery time is around five to six months, excluding complications."
Muntari, who joined Milan from Inter in January on loan, scored one goal in 14 appearances for the Rossoneri.