Djokovic withdraws from China Open

World No. 1 Novak Djokovic, citing a back injury, has withdrawn from next week's China Open tennis tournament. Djokovic said the back problem came up during the U.S. Open, which he ended up winning but often appeared to be in pain. He retired from a Davis Cup semifinal match the following week, a decision that sealed Djokovic's Serbian team elimination by Argentina. Djokovic is a two-time China Open defending champion. He took over the world No. 1 ranking after he defeated Rafael Nadal in the Wimbledon finals. Djokovic also beat Nadal in the U.S. Open final. He is 64-3 this year with 10 tournament titles, including a win at the Australian Open to go with his Wimbledon and U.S. Open major tournament championships. The China Open begins Monday.