World number-one Li Xuerui pulled out of the badminton Japan Open Wednesday because of a sore knee, with her teammate linking the problem to a jam-packed schedule for Chinese players.
The 22-year-old London Olympic champion suffered pain in her left knee and consulted the venue doctor before the Japan Open's first day, a tournament press official said.
The doctor, Takemasa Miyauchi, confirmed Li's knee trouble and the top-seeded Chinese player withdrew from the first-round match against Japan's Aya Ohori, the official said.
No more details on her knee problem were immediately available.
Li's male teammate Wang Zhengming told AFP: "Members of the Chinese team, including myself, have a tight schedule filled with matches."
"I think she (Li) probably had an old injury that was hurting again somewhat because of fatigue," he said through an interpreter.
Li, the 2012 All-England champion, was not immediately available for comment after limping out of the event, the eighth leg of the 12-round World Superseries and badminton's top-flight tour.