Spain's Rafael Nadal said he is suffering from a knee ailment known as Hoffa's syndrome but that he hopes to make a full recovery and is not worried about a further ranking drop after pulling out of the U.S. Open.

The 26-year-old tennis star unveiled the diagnosis in remarks to Efe from his hometown on the island of Mallorca, saying that his current knee injury - which is also known as fat pad impingement and involves pain and swelling around the bottom and under the kneecap - is different from his previous tendon ailments.

The injury forced the world No. 3 to pull out of four tournaments in succession: the London Olympics, two ATP World Tour Masters 1000 events in Toronto and Cincinnati and the U.S. Open.

Because he reached the final of the year's last Grand Slam event in 2011 and will be replacing those points with nothing, his ranking will almost certainly fall further in September.

But Nadal, whose ranking had already fallen from No. 2 to No. 3 because of an early exit from Wimbledon in late June, said his health is his top priority.

"At this point of my career (the ranking) is not the most important thing," Nadal, who held the No. 1 spot for just over a 100 weeks in two stints between 2008 and 2011, told Efe.

"Now the most important thing is to make a good recovery and right now my knee is not ready to compete in a Grand Slam; I'm going to try to recover as soon as possible to come back feeling strong, sure that I can compete and train the best that I know how," the Spaniard said.

The 11-time Grand Slam champion said what he most likes is to be able to push himself to the limit physically and "right now I'm not prepared for that."

Referring to the Davis Cup semifinals in September, when Spain will host the United States on clay in the northwestern city of Gijon, Nadal said he does not know yet if he will be able to compete and help his country continue its quest for a sixth title in that international team competition.

This week, his uncle and coach, Toni Nadal, said he was optimistic his nephew would be healthy in time for that competition.

The tennis star has not competed since his shock second-round exit from Wimbledon at the hands of unheralded Czech Lukas Rosol, considered one of the biggest upsets in the history of that prestigious tournament.

Nadal said his current injury is not the same as the rotulian tendon ailment he has suffered from in the past. "It's something different and I think this is good because the tendons are very well recovered compared to how they were three years ago."

The Spaniard began the summer on a high note by capturing a record seventh French Open title with a victory over then-world No. 1 Novak Djokovic of Serbia in the final.

Nadal, known for his physically demanding style of play and incredible defensive skills, has struggled to stay healthy during his career, having been forced to withdraw from each of the four Grand Slam events due to various injuries. 

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