The 27-year-old from Belarus, runner-up at the Australian and French Opens, comes off semi-final runs at Wimbledon and Berlin and titles at Madrid and Miami.

"I'm looking forward to kicking off the North American hard-court swing, but to give myself the best chance for success this season, I've decided it's in my best interest to skip Montreal," Sabalenka said.

Missing the July 27-August 7 event leaves the reigning US Open champion only one major tuneup, at Cincinnati in August, before she tries to defend her crown on the Flushing Meadows hardcourts.

"I'll miss my amazing Canadian fans, but I'm already looking forward to seeing you all next year," Sabalenka said. "Thanks for your understanding and support -- it means the world to me."

Sabalenka was upset in the Wimbledon semi-finals by American Amanda Anisimova.

"We're obviously disappointed that Aryna won't be with us this year," tournament director Valerie Tetreault said.

World number 10 Paula Badosa of Spain withdrew from the event due to injury. The two departures opened spots in the main draw for American Caty McNally and Japan's Moyuka Uchijima.

Canada's Eugenie Bouchard announced on Wednesday that she will retire from professional tennis after the WTA event in Montreal, her hometown.

Bouchard, 31, rose as high as fifth in the world rankings and enjoyed her best career season in 2014 when she reached her only Grand Slam singles final at Wimbledon.

She also made semi-final runs that year at the Australian and French Opens and reached the fourth round at the US Open, her best career showings in each of the Grand Slam tournaments.