French Open champion Rafael Nadal has pulled out of this week's Croatia Open due to tendonitis in his right knee.
The 19-year-old Spaniard aggravated the knee during his victory in the Mercedes Cup final in Stuttgart on Sunday, his eighth clay court title of the year.
"By itself, it's not so serious but could become so if I go playing from one tournament to another without rest," said Nadal.
"I am really sorry for not playing here where there are so many top players."
Despite the injury Nadal has joined world number one Roger Federer as the only men to have already qualified for the end of season Masters Cup in Shanghai.
"For me it's a dream. Now I'm among the eight best players in the world, which is very important to me," said Nadal, who has climbed to a career-best second in the world rankings.