Li Na pulls out of US Open

China's tennis superstar Li Na announced her withdrawal from the US Open due to her knee injury on Thursday.

"I'm sorry to inform I have to skip the upcoming Montreal and the Cincinnati event, as well as the US Open," Li wrote on her Sina Weibo.

"Since March, I have been struggling with my knee and it is just not where I need it to be in order to play at the highest level."

Li says her physio advised her to take a rest and that she expects to return when the tour comes to China, which includes a WTA Premier 5 event in her hometown Wuhan in September.

Li, 32, won the Australian Open earlier this year, her second Grand Slam title, but suffered early eliminations at both the French Open and Wimbledon.

The US Open will be played from August 25 to September 8.