Rafael Nadal withdrew from Spain's Davis Cup tennis final in Argentina because of tendinitis in his right knee.

The injury means the world No. 1 won't be fit enough to play in the Nov. 21-23 final, according to a statement on the official Davis Cup Web site. The matches will be played on an indoor carpet surface in Mar del Plata, Argentina.

"These are difficult moments, but I have done everything possible to try to make the final," Nadal said in the statement. "I am used to playing in pain, but this is a new and different pain that I am unable to control."

Nadal will end his most successful season on the sidelines and miss the chance of winning the men's team tournament with Spain a second time.

Spain could replace Nadal in singles matches with 16th- ranked Fernando Verdasco, or world No. 31 Feliciano Lopez, the team's regular Davis Cup doubles pairing. Another option is 19th- ranked Nicolas Almagro, who played his first Davis Cup match this year. Spain will announce the choice tomorrow.

Nadal, who missed this week's Masters Cup in Shanghai because of the injury, won Wimbledon, the French Open and the Olympic gold medal this year.

He also ended Roger Federer's record 237-week reign to become the top-ranked player for the first time.

After playing 93 singles matches this year, Nadal said last week that his workload may have harmed his physical condition as the season reaches a close.

"It's been a long year, very positive" apart from pulling out of this weeks's Masters Cup in Shanghai and the Davis Cup final, Nadal told a news conference today. "Sometimes that's how things turn out."

He underwent medical tests with Spanish tennis federation doctor Angel Ruiz Cotorro in Barcelona today before deciding to withdraw from the final. The deadline for announcing teams for the final is tomorrow.

Argentina, the beaten finalist in 1981 and 2006, is hosting the Davis Cup final for the first time. Spain is seeking a third title in the competition.

Nadal was 18 in 2004 when he upset Andy Roddick to help Spain beat the U.S. in the final in Seville. He was a ball boy in the 2000 final in Barcelona when Spain beat Australia.