Kim Clijsters of Belgium reacts during her match against Jie Zheng of China at the Rogers Cup women's tennis tournament in Toronto, August 9, 2011. [Photo/Agencies]

Champion Kim Clijsters has pulled out of the US Open due to a stomach muscle injury, the Belgian said in a statement on Friday.

"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," said the 28-year-old, three-times a US Open winner.

Clijsters suffered a partial tear of her left stomach muscle in Toronto earlier this month in what had been her first appearance since picking up a foot injury in June.

The four-times grand slam winner also said she would also have to skip tournaments in Japan and China scheduled for September and October.

"Now there is nothing else I can do than to rest and have treatment every day. If a gradual approach is not taken, I will relapse in the same injury, and therefore I have also no other possibility than to withdrawal from the tournaments in Tokyo and Beijing."

Clijsters also had to miss this year's Wimbledon Championships and she has suffered a series of injuries since she won the Australian Open in January.

In fact, the world number three has played only five matches over the past five months, during which she has nursed shoulder, wrist, ankle and foot injuries before suffering her latest setback.

The Belgian retired in May 2007 before marrying basketball player Brian Lynch and giving birth to a daughter.

She returned to the WTA tour in 2009 winning that year's US Open just weeks into her comeback.