Chelsea winger Jesper Gronkjaer has been ruled out for four months with a serious knee injury, according to reports in Denmark.

The former Ajax winger will have to wait until February to make a return as a result of the injury he picked up against Arsenal at the beginning of September, report Danish daily Ekstra Bladet. The new problem concerns the cartilage in his knee.

The Danish national team doctor Mogens Kreutzfeldt visited Gronkjaer in Brondby, Copenhagen, on Monday and the player met up with the rest of the national squad yesterday ahead of the vital World Cup qualifier against Iceland at the weekend.

"Jesper underwent an investigation on Monday afternoon. He should regain full fitness but there is a serious risk of him being brought back too soon after an injury like this," Kreutzfeldt said.

The Denmark international is now looking at a prolonged recovery comprising of long stints of cycling, swimming and general fitness training.

Gronkjaer, though, should be okay to take part in next summer's World Cup finals if he suffers no complications in his comeback bid.