Novak Djokovic of Serbia reacts during his Davis Cup World Group tennis semi-final match against Juan Martin Del Potro of Argentina in Belgrade Sept 18, 2011. [Photo/Agencies]

BELGRADE - World number one Novak Djokovic will miss next week's China Open in Beijing with a back injury, the 24-year-old Serb said on Thursday.

Djokovic, who won the Australian Open, Wimbledon and the US Open this season as he dislodged Rafa Nadal from the top of the world rankings, aggravated a niggling injury in Serbia's Davis Cup tie with Argentina earlier this month.

The strain he felt in his win over Nadal in the US Open final in New York became a rupture during his singles against Argentina's Juan Martin Del Potro, Djokovic retiring in anguish and sending the South Americans through to the final.

"I am very sad to announce I will not participate in the China Open," he told his website (www.novakdjokovic.rs).

"Because of my back injury, which is very particular and restrains me from rotating my upper body in serve motion, I am not able to compete," added the Serb who has won 64 of his matches this season.

"I apologise to all my fans and tennis lovers who bought tickets hoping to see me play. I am resting and doing a lot of therapies and trying to recover so I can play the remaining tournaments this season."

Apart from the three grand slam titles, Djokovic has won seven other tournaments this year including five Masters Series events, in his best season since he turned professional.

He has beaten Nadal six times in as many finals in 2011.

Djokovic said after Serbia's 3-2 defeat by Argentina in the Belgrade Arena that he hoped to recover in time for the China Open but then realised during a training session he was unfit to play.

"I have hit a couple of balls to test my body and unfortunately I still feel the pain," he said.