HALMSTAD, Sweden -- Wimbledon champ Novak Djokovic withdrew from his scheduled singles match on Friday in the Davis Cup quarterfinals for Serbia against Sweden because of a knee injury.

Djokovic was slated to take on Ervin Eleskovic in the second of Friday's opening singles matches. He will be replaced by Janko Tipsarevic.

The recently-anointed world No. 1 could still return for reverse singles on Sunday.

Djokovic led Serbia to the Davis Cup title last December and has carried that momentum into a sensational 2011 season that started with a title at the Australian Open. He has lost just once all year, a semifinal setback to Roger Federer at the French Open, and has won an incredible eight titles. Most recently, he defeated Rafael Nadal for the Wimbledon crown just five days ago at the All England Club for his third career Grand Slam championship.