World number one Novak Djokovic on Thursday pulled out of the China Open with injuries he aggravated during Serbia\'s Davis Cup semi-final defeat, the tournament website said. The Serb, who had needed treatment on his back during his US Open final win, could be joined as an absentee from next week\'s WTA-ATP tournament by Maria Sharapova. The second-ranked Russian rolled her ankle on Thursday in a Tokyo loss to Petra Kvitova and quit trailing 4-3 in their quarter-final. Djokovic was told by doctors after the Davis Cup semi-final earlier this month that he would need a month of rest. But he was seen running around a Belgrade football pitch this week in a charity exhibition match. His participation in the Shanghai Masters starting on October 9 appears to be in doubt. World number three Roger Federer has already withdrawn from that event due to injury, insisting he needs rest after a gruelling year. Frenchman Richard Gasquet is also out as he battles a wrist injury, organisers said. Gasquet suffered the injury playing in the Davis Cup semi-final loss to Spain though he played through the pain barrier in reaching the last eight on home ground at Metz last week.