Chinese No. 1 Li Na has pulled out of a domestic tournament because of the recurrence of an injury that could prevent her from playing at the US Open.

The 27-year-old felt her right knee injury return after a few matches of the team preliminaries for China's National Games in Shandong Province, where she was representing her Hubei Province.

The world No. 18 would have tests in Beijing to determine whether she will be able to play in the North American hardcourt season, including the August 31-September 13 US Open, according to her husband and coach Jiang Shan.

"We have signed up for it and got the visa. If she is okay by then we will go to play," Jiang told the Beijing Youth Daily.

"If not, we would have to go rehabilitation first."

If the injury was serious, they would consider going to Germany for treatment, Jiang added.

Li withdrew from Brisbane, Sydney and the Australian Open at the beginning of this year because of the same problem and again at the Strasbourg and Eastbourne tournaments in May.

The former Wimbledon quarterfinalist, who has suffered from repeated injuries since returning to tennis in 2004 following a 25-month break from the sport, said she wanted to finish at least one season without injury.

Five-time defending champion Roger Federer, Rafael Nadal and Andy Roddick are among eight grand slam winners leading the men's field for the US Open.

All top 100 men in the rankings received direct entry on Wednesday.

Federer will be trying to become the first man since Bill Tilden in the 1920s to win the American grand slam tournament six consecutive times. By winning the French Open and Wimbledon this year, Federer raised his career total to 15 major titles, breaking Pete Sampras' record of 14. Nadal missed Wimbledon with sore knees and hasn't played since late May.

(Agencies via Shanghai Daily July 24, 2009)