Novak Djokovic pulls out of China Open

BEIJING -- Top-ranked Novak Djokovic has pulled out of the China Open because of a back injury.

Tournament organizers said the defending champion withdrew because the latest medical checks show the injury he sustained while winning the U.S. Open has not yet healed.

The tournament in Beijing starts on Monday. It is not yet clear whether the 24-year-old Serb will also skip the Shanghai Masters that starts in two weeks.

Djokovic has said the partial rupture of a back muscle that forced him to quit his Davis Cup semifinal match against Argentina's Juan Martin del Potro is not serious, but requires rest.