Andy Murray has pulled out of the third round of the Rogers Cup with a knee injury.

The Olympic gold medalist says he hurt his left knee during the opening match against Flavio Cipolla of Italy. Murray was to play Canadian Milos Raonic on Thursday night.

Murray says he's unsure whether he will play in the ATP Tour's next stop in Cincinnati or the upcoming U.S. Open.

His withdrawal follows a string of pullouts at the Rogers Cup in Toronto. Roger Federer and Rafael Nadal withdrew before the tournament began.