Two-time defending champion Kim Clijsters has withdrawn from the US Open after failing to recover from a stomach muscle injury.
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.
Clijsters said: "Unfortunately I will not be able to defend my US Open title this year because of a stomach muscle injury. Two weeks of rehab was not enough to heal this injury.
"Obviously I'm very disappointed. I trained very hard this summer and felt in a good shape to play the US Open."