World number one Novak Djokovic has pulled out of next week's Shanghai Masters due to a persistent back injury.
The Serbian had to miss his title defence in last week's China Open because of the same problem.
"I am sorry not to be playing in Shanghai, one of my favorite tournaments, but I have not recovered yet from my injury," said the 24-year-old.
"I did another check this week and the results are not good so I need to continue my rehabilitation.
Djokovic, who has won the three of the four Grand Slams this year, aggravated the injury representing Serbia in their Davis Cup defeat to Argentina last month.