JINAN, East China, Oct. 21 (Xinhua) -- Chinese tennis star Li Na was forced to quit the on-going 11th National Games due to knee injury in her first singles match Wednesday.

    After losing the first set 0-6 to Chen Yanchong of Guangdong, Li, the nation's No. 1 and also the world No. 16, called off the game, and walked out of the court accompanied by her husband.

    The 27-year-old Li, who had long sustained right knee ligament sprain, withdrew from the team event that was held earlier in July because of the same problem.

    "It was difficult for Li to walk after the first set, and apparently she could not continue her match," the head umpire, Wang Li, told Xinhua after the match.

    "That means she can no longer compete for this tournament," Wang said.

    Li is the nation's top tennis women's singles player. She snatched three titles in the singles and doubles events at the ninth National Games in 2001, and led her team to the final victory at the tenth Games four years ago.

    Li has claimed more than 20 singles titles since she started her professional career a decade ago, including the first WTA Tour singles title by a Chinese woman in 2004.