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.
Li, who bowed to Thailand's Ratchanok Intanon in the August 11 world championship final in Guangzhou, China, also lost to another Thai, Porntip Buranaprasertsuk in the semi-finals of the most recent previous Superseries event, last week's China Masters.
Between the two international contests, Li also played in the Chinese National Games in Liaoning, claiming the women's gold medal.
The packed playing schedule has been a universal concern for badminton stars, with the men's world number one, Lee Chong Wei of Malaysia, being advised to reduce his tournament appearances in order to continue his career toward the 2016 Rio de Janeiro Olympics.
"I have been playing in so many tournaments," the 30-year-old men's top-seed said on Tuesday. "But I have adjusted the number of tournaments I play," adding that he skipped the China Masters to focus on the Japan Open.
"As I have said every year, the Japan Open is the most important tournament for me as it is an event of my biggest sponsor," he said, referring to a Japanese sportswear and gear maker.
Lee, who has already won the Opens in South Korea, Malaysia, India and Indonesia this year, is going for a record fourth Japan Open men's singles title.
He will then have a two-week stint in the Chinese Super League for Guangzhou before taking part in the remaining four Superseries events in Denmark, France, Hong Kong and China (China Open).
Lee was stretchered from the court during last month's world championships final against his archrival, China's Lin Dan, with cramp and dehydration.
Badminton officials at home urged him afterwards to cut down his schedule.