MADRID, Spain -- Rafael Nadal pulled out of the season-ending Masters Cup in Shanghai on Monday, citing fatigue after a long season and the need to prepare for the Davis Cup final.
The world's top-ranked player made the announcement on his Web site, describing his withdrawal as "one of the most difficult decisions in my career."
Nadal, who won two Grand Slam titles and the Olympic gold medal this year as he supplanted Roger Federer at No. 1, said he was physically run down.
"It has been a long and difficult year where I managed to obtain great results, both on a professional and on a personal level," he said. "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" for each event.
The Spaniard, winner of a fourth straight French Open title and first Wimbledon championship this year, withdrew from the Paris Masters last Friday with a knee problem after losing the first set of his quarterfinal match against Nikolai Davydenko.
"On a personal level I had as one of my goals to become No. 1 during this year and competing at so many events might have harmed, especially at the end of the season, my physical condition, taking away the freshness needed to play at the top level of the game in these last events," Nadal said.
Nadal also said he hoped that his absence would buy him time for the Davis Cup final against host Argentina from Nov. 21-23.
"I want to recover and be ready for the important Davis Cup final with my country that will be played in Mar del Plata, Argentina. That is also another reason for not coming to Shanghai," Nadal added.
Nadal will be replaced in Wednesday's draw in Shanghai by Frenchman Gilles Simon.
The Spaniard's absence should boost the chances of Federer of winning his fifth Masters Cup, following his triumphs in 2003, 2004, 2006 and 2007.
Frenchman Jo-Wilfried Tsonga clinched the final singles berth at the Masters Cup by winning the Paris Masters title on Sunday.