MADRID, Spain (AP) -- Rafael Nadal has tendinitis in his right knee and could be in doubt for Spain's Davis Cup final against Argentina later this month.<!--startclickprintexclude--><!-- PURGE: /2008/SPORT/11/04/tennis.masters.ap/art.nadal.afp.gi.jpg --><!-- KEEP -->
<!--===========CAPTION==========-->Nadal withdrew from the Paris Masters last Friday with a knee problem after losing the first set.<!--===========/CAPTION=========-->
Medical tests Tuesday confirmed the condition, and Spain team doctor Angel Ruiz-Cotorro said the top-ranked player would undergo treatment through Saturday.
Nadal will have further tests on Monday to assess the injury.
Spain play Argentina in the final on indoor hard court at Mar del Plata from November 21-23.
Spanish Davis Cup captain Emilio Sanchez Vicario will not pick Nadal if he is unfit, Nadal's uncle and coach Toni said earlier Tuesday.
On Monday, Nadal pulled out of the season-ending Masters Cup in Shanghai citing fatigue after a long season in which he's played in 111 matches.
Nadal, 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.
Nadal won two Grand Slam titles and the Olympic gold medal this year as he supplanted Roger Federer at No. 1. Without Nadal, Spain would be regarded as a big underdog to lift their third Davis Cup trophy in eight years.
Spain beat the United States 4-1 in the semifinals, with Nadal and David Ferrer playing singles and Feliciano Lopez and Fernando Verdasco the doubles.
Meanwhile, French player Gilles Simon says he would have preferred to qualify directly for the season-ending Masters Cup rather than relying on Nadal's withdrawal.
Nadal pulled out of the prestigious season-ending tournament in Shanghai on Monday citing fatigue and the need to prepare for the Davis Cup final. The Masters Cup, beginning Sunday, features the top eight players in the ATP race.
"I was unhappy that he had to pull out," first reserve Simon said Tuesday. "I would really have preferred to qualify directly by finishing eighth. It's not in my nature to wish that another player can't play."
Even without Nadal playing, Simon is preparing himself for a tough mental challenge at the tournament.
"I will only be playing against very, very good players in Shanghai. You have to keep your head to win these games," Simon said. "You won't beat players like (Roger) Federer or (Andy) Murray if you're just happy to be on the court."
Simon made a late run for Shanghai by reaching the Madrid Masters final last month -- beating Nadal on home soil in the semifinal -- and also by reaching the last four at Lyon to add to titles he won at Casablanca, Indianapolis and Bucharest.
"It became possible for me after my final in Madrid," Simon said. "I'm really happy to be going there and I really want to experience this."
Richard Gasquet was the only French player at last season's Masters Cup, but this time Simon will be joined by Jo-Wilfried Tsonga, who took the final place by winning the Paris Masters on Sunday.
Simon is close friends with Tsonga, the Australian Open runner-up, and wants to avoid playing him in the group stages.
Lennart Bergelin, the Swedish tennis coach who trained Bjorn Borg for 12 years and captained the country to its first Davis Cup title, has died. He was 83.
Peter Bengtsson, a spokesman for the Swedish Tennis Association, said Bergelin died from heart failure at a Stockholm hospital early Tuesday morning.
As a player, Bergelin won nine Swedish championship singles titles between 1945 and 1955, and the French Open doubles title in 1948. But he became more famous for his work with Borg, whom he trained between 1971 and 1983, helping the Swede win 11 Grand Slam tournaments.
"He was nearly like a dad to Bjorn Borg," Bengtsson said. "But you shouldn't forget that he was also a very good tennis player before tennis was as professional as it is now."