China’s Li Na, Asia’s only grand slam singles champion, announced her retirement from tennis yesterday, citing the effect of long-term injuries, especially her knees.

“It has been a difficult year, and I have had to face a lot of things, such as making the decision to end my professional tennis career,” Li said in a statement.

The 32-year-old won the 2011 French Open and this year’s Australian Open.

Known affectionately as ‘Big Sister Na’ and ‘Golden Flower’ in China, she said it was the right time to leave the court.

“As a professional tennis player, leaving the field of competition at this moment is for me the correct decision,” she added.

The pain in her right knee had become hard to deal with, Li said.

“Competition is fierce and requires athletes to be at their best. As for me, I can no longer get back to being 100 per cent,” she added.

The Chinese Tennis Association, in a statement released by the official Xinhua news agency, said it respected her decision and wished her the best.

“We also thank Li Na for the passionate and proud, shining moments she gave to Chinese tennis in her competitive career,” it said.

For many young people in China, Li is a role model, with her steely determination, broad smile and English language skills emblematic of a confident and rising country.

During her career, she won nine WTA events, including the two grand slam titles, and reached number two in the world rankings.

She earned more than $16 million in prizemoney and much more in endorsements and sponsorship, becoming one of the world’s highest-earning female athletes.