Manacor, Spain - Rafael Nadal was Tuesday facing a massive fitness fightback after being diagnosed with tendinitis in his right knee.

Doctors said that the 22-year-old world number 1 will need nearly a week of physiotherapy treatment and rest, with a further evaluation on his troublesome knee to be made early next week.

Nadal's dream is to lead Spain in the November 21-23 Davis Cup final in Argentina.

Already, the four-time French Open champion has had to withdraw from the Masters Cup in Shanghai, starting on Sunday.

Nadal clawed his way to eight titles this season, including a first-ever Wimbledon where he beat Federer in a classic marathon.

Both Nadal and Federer pulled out of the Paris Masters last week at the quarter-final stage.

Spanish Davis Cup team doctor Angel Ruiz-Cotorro said in a statement that Nadal will be able to resume training perhaps as early as next week if he no longer feels pain.

More tests are set for Monday, second day of group play in Shanghai. Nadal is resting at home on the island of Mallorca. (dpa)