Chelsea striker Didier Drogba has undergone surgery on his persistent knee injury.
Drogba has shown impressive from for Chelsea this season
The 29-year-old Ivory Coast captain now faces a race to be fit for the African Cup of Nations in January and February.
Chelsea boss Avram Grant had been uncertain when the operation would take place, but Drogba suffered a recurrence of his injury in training on Friday.
Drogba has scored nine goals in 15 appearances for Chelsea this season and his absence is a major setback.
He misses Saturday's game against Sunderland at Stamford Bridge and Tuesday's game against Valencia in the Champions League, in which they have already qualified for the knock-out stages.
Chelsea then face Premier League leaders Arsenal on 16 December, but they have not specified how long he will be missing.
Club doctor Bryan English said: "Didier's knee locked on Friday afternoon and the decision was taken to have the operation immediately in the medical interests of the player.
"The procedure went well and he will begin his rehabilitation as soon as possible."

Drogba has shown impressive from for Chelsea this season
The 29-year-old Ivory Coast captain now faces a race to be fit for the African Cup of Nations in January and February.
Chelsea boss Avram Grant had been uncertain when the operation would take place, but Drogba suffered a recurrence of his injury in training on Friday.
Drogba has scored nine goals in 15 appearances for Chelsea this season and his absence is a major setback.
He misses Saturday's game against Sunderland at Stamford Bridge and Tuesday's game against Valencia in the Champions League, in which they have already qualified for the knock-out stages.
Chelsea then face Premier League leaders Arsenal on 16 December, but they have not specified how long he will be missing.
Club doctor Bryan English said: "Didier's knee locked on Friday afternoon and the decision was taken to have the operation immediately in the medical interests of the player.
"The procedure went well and he will begin his rehabilitation as soon as possible."