Chelsea midfielder Michael Essien has been ruled out of action for "several months" after rupturing his anterior cruciate ligament, the club announced on Tuesday.

The 25-year-old sustained the injury while on international duty with Ghana and a Chelsea statement said: "Michael has ruptured his anterior cruciate ligament and will undergo an operation as soon as the majority of the swelling has subsided. We expect this to happen in a week's time.

A return to full fitness is not expected for several months
A statement from Chelsea Football Club.

"In the meantime, Michael has started rehab in the aqua therapy centre at Cobham (Chelsea's training ground south of London) which will improve the condition of the knee prior to surgery. ."

The news he will miss a major chunk of the season is a major blow to a club which suffered a series of injury woes last season as the Blues ultimately failed to keep pace with English Premier League champions Manchester United.

The industrious Ghanaian joined Chelsea in 2005 from French side Lyon and signed a new five-year deal in July.