Kim ClijstersThe U.S. Open has lost three-time and defending champion, Kim Clijsters. She informed tournament officials Friday that she would be unable to participate in the season’s final major because of a strained abdominal muscle.

Clijsters, who missed Wimbledon with an ankle injury, pulled out of a tournament in Toronto this month with a muscle strain on the left side of her stomach. In a statement Friday, she said “two weeks of rehab is not enough to heal this injury.”

“Obviously I’m very disappointed,” she said. “I trained very hard this summer and felt in a good shape to play the U.S. Open.”

Clijsters, 28, ranked No. 3 in the world, said she would also pull out of tournaments in Japan and China in September.

Clijsters claimed her first major at the U.S. Open, winning the title in 2005. Her victory in 2009 was particularly impressive, coming within months of her return to competition after taking two years off to marry and start a family. Clijsters’s daughter, Jada, joined her mother for the on-court trophy presentation that followed. Mother and daughter accepted last year’s trophy together, as well. She became the first unseeded woman to win the U.S. Open and the first mom to win a major since Evonne Goolagong Cawley won Wimbledon in 1980.

Last year, Clijsters repeated at Flushing Meadows. She won the Australian Open this year for her fourth Grand Slam title.