New world No. 1 Novak Djokovic is forced out of his Davis Cup singles match against Sweden’s Ervin Eleskovic with a knee problem. Before winning Wimbledon, Djokovic pulled out of Queen's Club with knee trouble. Janko Tipsarevic replaced Djokovic and was leading 6-2, 1-0 when Eleskovic retired. Serbia's Victor Troicki won his opening match, and if defending champion Serbia wins the tie, they will have a home match against Argentina, which shut out Kazakhstan 3-0 at home.