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Novak Djokovic returns a shot during his final round in the men's final at Wimbledon on July 3. ((Stephen Pond/Pool/Getty Images))

Top-ranked Novak Djokovic has withdrawn because of a left knee injury from his singles match for Serbia against Sweden in the Davis Cup quarterfinals.

The Wimbledon champion will be replaced by Janko Tipsarevic, who will face Ervin Eleskovic. Sweden's Michael Ryderstedt will play Viktor Troicki in the opening match on Friday.

It was unclear whether Djokovic would be back for the reverse singles on Sunday.