World number two Li Na of China will miss the US Open with a knee injury.
The 32-year-old, who won the Australian Open earlier this year for her second Grand Slam title, has targeted a return to action in late September.
"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 said on Facebook.
The US Open starts on 25 August in New York and Li will miss the WTA events in Montreal and Cincinnati as well.
"My medical team has advised me that I need to take some time off to rest my knee so it heals," added Li, whose first Grand Slam title came at the 2011 French Open.
Li was eliminated from this year's French Open in the first round before bowing out of Wimbledon in round three.