Rafael Nadal has withdrawn from the National Bank Open in Toronto due to a lingering foot injury.
The world No 4 lost in the third round in Washington last week on his return to competitive tennis after a two-month absence.
Nadal, 35, withdrew from both Wimbledon and the Tokyo Olympics in an effort to prolong his career.
"I really wanted to play here a lot, but now is the moment to make a decision, and this is unfortunately the decision that I have taken," said Nadal, who is a five-time winner of the Masters 1000 event in Canada.
Nadal said a recurring foot injury that has troubled him since 2005 reappeared at the French Open, where he was beaten by eventual champion Novak Djokovic in the semi-finals.
"I have had this issue for a couple of months, as people know," added the 20-time Grand Slam champion.
"Of course, it is not a happy situation after all the success that I had here in Canada, not being able to play this year after missing a year. It's a tough one, but that's how it is today."
Nadal's withdrawal hampers his preparation for the US Open, which begins in New York on August 30.
World No 1 Djokovic withdrew from next week's Western & Southern Open in Cincinnati on Monday to enhance his bid to secure a calendar Grand Slam.
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