Madrid - Rafael Nadal has withdrawn from next week's Toronto Masters Series hardcourt tournament, the Spanish world No 3 confirmed on Thursday.
The 26-year-old's announcement follows his decision not to defend his title at the London Olympics, and throws into doubt his participation in the US Open which gets underway at Flushing Meadows in New York on August 27.
"Hi all, wanted to let you know that I won't be playing Toronto this year," Nadal wrote on his Twitter account.
"I am not ready to play and I hope to be back in 2014 at that great tournament that has always treat me very well. I am continuing with my recup and practice. Thanks!"
Nadal pulled out of the Games after claiming he was "not in condition" to compete following a recurrence of the knee problems which have troubled him for several years.
He had struggled with the injury throughout his French Open title-winning campaign and looked well short of his best in a stunning Wimbledon second round defeat against unheralded Czech Lukas Rosol.
Nadal added in a statement: "Coming to Toronto is always one of the highlights of my season so I'm very disappointed that I can't play there this year.
"I was planning on coming to Toronto and did everything I could to be ready but I still need some more time to recover."
It will be the first time since his debut appearance in 2004 that Nadal will miss the Canadian Masters event which he won in 2005 and 2008.
Additional main draw withdrawals include Spaniards David Ferrer and Fernando Verdasco and France's Gael Monfils.