Maria Sharapova has pulled out of this week's Rogers Cup after failing to recover from injury, tournament organisers announced.
The Russian, who will become world number one on August 22, injured a right pectoral muscle on Friday in Los Angeles, forcing her out of her quarter-final against Daniela Hantuchova.
Sharapova will take over as number one regardless because top-ranked American Lindsay Davenport has missed four straight tournaments with a back injury.
"I have to take care of my body for the US Open," said the 18-year-old.
"It's a grand slam and that's where you always want to be ready."
The Rogers Cup in Toronto features former world number ones Justine Henin-Hardenne, Amelie Mauresmo and Serena Williams.