Defending champion Kim Clijsters has withdrawn from the US Open with a stomach muscle injury.
"Unfortunately, I will not be able to defend my US Open title this year," the Belgian, a three-time winner at Flushing Meadows, said in a statement.
"Two weeks of rehab was not enough. Obviously I'm very disappointed. I trained very hard this summer and felt in a good shape to play."
The final major of the year starts on Monday 29 August.
It has been an injury-hit season for the world number three, who missed most of the clay-court season and Wimbledon with an ankle injury before being forced out of last week's tournament in Toronto with the stomach problem.
"Now there is nothing else I can do than to rest and have treatment every day," added the 28-year-old.
"If a gradual approach is not taken, I will relapse, and therefore I have also no other possibility than to withdraw from the tournaments in Tokyo and Beijing."