"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,'' Federer said on his Web site Friday. "As a precaution and because I would be unable to play at 100 percent tonight, I have unfortunately had to take the difficult decision not to play.''
Federer apologized to the disappointed fans who came to watch him at the Bercy indoor arena.
"This is the first time ever I've pulled out during a tournament, so it feels bad,'' he said. "I don't like to do it. Feel bad for the tournament and for the fans.''
Federer said he hopes the injury will only take a few days to recover and that he will be able to play in the season-ending Masters Cup in Shanghai which begins Nov. 9.
"Usually the back is something that takes a few days and it's better again,'' Federer said. "I'm confident and I'm positive that hopefully it's going to get better in the next few days.''
The 13-time Grand Slam champion has never reached the semifinals at the Bercy indoor arena after losing in the 2002 and 2003 quarterfinals.
The 11th-seeded Blake now advances to the last four, where he will face either No. 7 Andy Roddick or No. 13 Jo-Wilfried Tsonga, who played later.
Federer said he first felt a surge of pain when serving during his second-round match against Robin Soderling on Wednesday. The pain subsided overnight but came back in the third round against Marin Cilic when he lunged to retrieve a shot.
"Usually overnight and maybe with painkillers you sort of get over it, but I just feel like I just can't play the way it is right now,'' Federer said. "I mean, you can hit balls but you can't play professional tennis against the best in the world.''
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