(REUTERS) - Maria Sharapova's US Open preparations took a major blow, with the Russian world No. 2 forced to withdraw from next week's WTA event in Toronto.

The 28-year-old Russian withdrew due to a right leg strain, the tournament organisers said on Friday.

Sharapova has not played since she lost to world No. 1 Serena Williams in the Wimbledon semi-finals on July 9 and has played just 10 tournament so far this year.

The Rogers Cup in Toronto is a key stop on the North American hard-court circuit before the year's final Grand Slam at Flushing Meadows in New York from Aug 31 to Sept 13.