LONDON - Chelsea midfielder Michael Essien will be out for up to six weeks with the knee injury that forced him out of the African Nations Cup, manager Carlo Ancelotti said on Friday.

Essien was injured during a training session with his Ghana squad in Angola on Sunday and medical checks made by the Ghanaian staff later showed the injury was worse than first feared, forcing him to leave the tournament early.

"He had a tear in the meniscus, and he has to stay out for four to six weeks,' Ancelotti said. "I hope four," he told reporters ahead of Chelsea's FA Cup fourth round match at Preston North End at the weekend.

Ancelotti said he will not be going into the transfer market to buy a replacement.

Essien has had a miserable time recently and has not played for Chelsea since their Champions League game against APOEL Nicosia on December 8 when he scored an early goal but was forced off with a hamstring injury midway through the first half.

He then joined his team mates late in Angola after bad weather had delayed his departure from London and only played for 45 minutes against Ivory Coast last Friday.