Belgium's Kim Clijsters has pulled out of this week's China Open due to fitness problems, tournament officials said on Tuesday.

The reigning U.S. Open champion is the second top star after world number one Serena Williams to withdraw from the joint WTA/ATP tournament, which runs from October 2 to 10 in the Chinese capital.

Clijsters said in an e-mail to the China Open organizing committee that she could not make the trip as she continues to recover from recent surgery on her right foot after winning her third U.S. Open title.

The 27-year-old Belgian apologized in the e-mail to her fans in Asia, promising to play in Beijing next year.

Serena Williams cut her foot on broken glass at a restaurant shortly after winning her fourth Wimbledon crown in July and has not played since.

Earlier this month, China's Zheng Jie also withdrew with a wrist injury that could rule her out of action for the rest of the year.

Other major stars in the women's game expected to play in Beijing include Venus Williams, Maria Sharapova and Caroline Wozniacki.