(CNN) -- Roger Federer, hampered by a back injury in recent weeks, pulled out of the Rogers Cup in Montreal with the U.S. Open just around the corner.
"I am disappointed not to be playing in Montreal next week," Federer said in a tournament press release sent to CNN. "It is a great tournament with amazing fans. I look forward to competing there in the future."
Although no reason was given for his absence, Federer said after a surprise defeat to Daniel Brands in his native Switzerland last week that he had been having "serious problems" with the back and needed to take anti-inflammatory medication.
The withdrawal continues a disappointing spell for the 17-time grand slam champion, who turns 32 on Aug. 8.
Federer appeared to be headed in the right direction going into Wimbledon when he won his first title of 2013 in Halle, Germany on grass.
But Federer was upset in the second round by Sergiy Stakhovsky at the All England Club, marking the first time he failed to advance to the round of 32 at a major since 2003.
When the new rankings were released after Wimbledon, he dipped to No. 5, his lowest position in 10 years.
Federer decided to enter tournaments in Hamburg, Germany and Gstaad, Switzerland with a larger racquet -- a significant change for a tennis player -- but lost to opponents outside the top 100 and top 50, respectively.
"A change like this is very important but I honestly can't tell right now due to my low level," Federer said in Gstaad, when asked about the new racquet. "It's hard to analyze anything.
"I still don't have even enough information to try and explain. I have no clue where I am right now with the racquet change."
If Federer plays at the U.S. Open -- which begins Aug. 26 -- he would participate in a 56th consecutive grand slam tournament, tying the men's record in the Open era.
As one double-digit grand slam winner skipped Montreal, another is set to return.
Rafael Nadal arrived in the Canadian city having not played since a first-round loss to Steve Darcis at Wimbledon.
Nadal has been troubled by his knees this season, despite winning the French Open in June. He returned to the tour early this year following a seven-month layoff.
"I will try to arrive competitive in Montreal because seven weeks without playing isn't ideal for competing in such a difficult tournament," Nadal was quoted as saying by the ATP's website. "But I'll do everything possible for things to go well."
Andy Murray plays his first tournament, too, since ending Britain's 77-year wait for a men's singles winner at Wimbledon.
Novak Djokovic, Murray's opponent in the Wimbledon final, is the top seed in Montreal.