World number two Roger Federer has pulled out of the Paris Masters with a back injury just before his quarter-final against American James Blake.
"Due to a stiff back, I have decided to pull out of my match against James Blake tonight," the Swiss said in a statement on his official website.
"My back has been stiff for the last couple of days and I woke up this morning and it did not respond to the treatment I had last night.
"As a precaution and because I would be unable to play at 100 per cent tonight, I have unfortunately had to take the difficult decision not to play."
Federer's withdrawal means the Swiss has failed to win a regular Masters Series event this year for the first time since 2003.
Federer is next scheduled to play in the season-ending Masters Cup in Shanghai, which starts on 9 November.