Britain's world number one Andy Murray has withdrawn from the Rogers Cup as he has yet to recover from the hip injury which hampered his Wimbledon campaign.
The 30-year-old Scot said he was "disappointed" to miss next week's tournament in Montreal and Toronto, but added: "I am doing everything I can to return as quickly as possible."
Murray could lose his number one ranking to Rafael Nadal next week, and he remains a doubt for the US Open, which begins on 28 August.
Earlier on Thursday, five-time Grand Slam champion Maria Sharapova withdrew from the event, and Tennis Canada confirmed world number six Marin Cilic has also pulled out.
Nadal and Roger Federer will now be the top two seeds in the men's draw, with Stan Wawrinka also absent.
Murray is next scheduled to play the Cincinnati Masters from 14 August.