The injury that forced 2008 ­champion Rafael Nadal to pull out of this year's Wimbledon may put an end to the 23-year-old's career, according to sport scientists. The Spaniard has ­suffered with tendinitis of both knees since the age of 21 and leading tennis coach Sven Groneveld said yesterday that he has never known a player to be so badly afflicted with the injury so young.

"I think he is quite a unique case," said the coach of Ana Ivanovic and Fernando Verdasco. "It's bad enough for him not to play and defend the title. It must be very, very hurtful, besides the pain in the knees."

Nadal said pulling out of the Championships two days before he was due to open play on Centre Court was the "worst decision" of his career and it is likely the patella tendinitis contributed to his relinquishing of the French Open crown for the first time in five years.

Sean Corvin of Premier Training, the health and fitness educator, speculated that the world No1's knees are those of a 33-year-old. "A large number of athletes may have retired early because of this condition and some may be ­performing at a lower level because they can't ­tolerate the heavy training," he said.

The six-times grand-slam winner is being treated with oral anti-­inflammatory medication as well as physiotherapy and progressive muscular exercises, but ­irreversible damage may have been done at a young age and Groneveld believes the prevalence of hardcourts is a factor.

"When kids play on hard surfaces from a young age, it has something to with their growing, [which] increases the chance of getting it," said the Dutchman. "During the growth it is not good to play on hard surfaces."

The prospect of playing the gruelling kind of match that Tommy Haas concluded against Marin Cilic yesterday with a victory that took four and a half hours must have been a factor in Nadal's decision to withdraw.