Barcelona, Spain -- (Sports Network) - Rafael Nadal will not play in the Davis Cup final for Spain later this month against Argentina because of a lingering knee problem.

The injury forced the world's top-ranked player to pull out of the Paris Masters a few weeks ago and also caused him to skip this week's season-ending Tennis Masters Cup in Shanghai.

"After a very long and positive year, it is terrible to not be able to participate at two big goals of the year, Shanghai and the Davis Cup final," Nadal said Monday. "These are tough moments, but I have done everything possible to be fit for the final. It was something I really wanted. I am used to pain, I am used to playing with pain, but this one is different -- new that I can't control."

Nadal, who posted a pair of singles victories to guide the Spaniards past the United States in the Davis Cup semifinals, underwent tests Monday and it was determined that he would not be able to compete next weekend.

The Spanish superstar had a banner 2008 season, surpassing Roger Federer as the world's No. 1 player. He captured the French Open for a fourth consecutive year and finally ended Federer's reign at Wimbledon in one of the most compelling finals at the All England Club in July.

In addition to the Grand Slam victories, Nadal also won Olympic gold in Beijing while capturing five other tournament titles. He will end the year as the top-ranked player for the first time.