UFC bantamweight champion Dominick Cruz, who has not fought since October 2011 due to injury, underwent surgery for a second time last week to repair a torn anterior cruciate ligament.
Cruz is expected to be out of action indefinitely.
Cruz, who suffered the injury in May while preparing to defend his title against Urijah Faber, underwent surgery in July. He was scheduled to face Faber on July 7.
MMAJunkie.com reported Cruz's second surgery earlier on Monday.
Cruz (19-1) was expected to meet with doctors on Monday for a progress report and learn when he can reasonably hope to return to the Octagon.
Cruz last defended his title on Oct. 1, 2011, when he defeated Demetrious Johnson by unanimous decision. After the fight, Johnson dropped to flyweight, where he captured that division's championship belt.
With Cruz unable to perform in July, Faber faced Renan Barao for the interim 135-pound title. Barao defeated Faber by unanimous decision on July 21.