World number one Rafael Nadal pulled out of the season-ending Masters Cup on Monday because of injury.
The Spaniard was forced to retire from his Paris Masters quarter-final against Russian Nikolay Davydenko last week because of a knee problem and said the packed tennis calendar had taken its toll on his body.
"I have decided not to compete at the Masters Cup in Shanghai," Nadal said in a statement on his website (www.rafaelnadal.com).
"I have mentioned on various occasions that the tennis calendar has been extremely hard with practically all weeks playing and where it forces players to compete week in week out, making it impossible for a top-level player to be 100 percent on each event," he said.
"Competing at so many events might have harmed, specially at the end of the season, my physical condition, taking away the freshness needed to play at the top level of the game on these last events."
Nadal, who the ATP said would be replaced in Shanghai by Frenchman Gilles Simon, said he was hoping to be fit for Spain's Davis Cup final against Argentina later this month.
"I want to recover and be ready for the important Davis Cup final with my country," said Nadal, who replaced Swiss Roger Federer as number one in August.
"That is also another reason for not coming to Shanghai. I know that many people were speculating with this news and even though I have yet not done any test, I can say I take the right decision."