Li withdraws from U.S. Open

New York, NY ( - World No. 2 star Li Na has withdrawn from the upcoming U.S. Open, citing a knee injury.

The two-time Grand Slam champion from China will also miss the big hardcourt events in Montreal and Cincinnati over the next two weeks.

Li said her knee has been bothering her for four months "and it is just not where I need it to be in order to play at the highest level."

The 32-year-old captured the Australian Open in January and was the French Open champion three years ago. Li was a semifinalist at last year's U.S. Open.

The 2014 U.S. Open will begin Aug. 25 in New York.