Knee injury forces Andy Murray from Toronto

Olympic champion Andy Murray was forced to withdraw from the Toronto Masters on Thursday with a knee injury, sending Canadian Milos Raonic into the quarter-finals of his home event.

Murray, who won a struggling second-round match on Wednesday after arriving in Canada on Tuesday from his gold-medal performance at the London Games, was treated for the knee during his victory over Italian Flavio Cipolla.

The pullout came on a day of rain which prevented the start of third-round play.

Murray, twice a champion in Canada, will hope to be fit for a title defence starting next week in Cincinnati, the last major tune-up before the August 27 start of the US Open.

"I decided this morning," said Murray. "It was a bit sore yesterday. I came in today, saw the physios, they did some work on it, and it's still a bit sore.

"I did a little warmup on the bike to try it out and it was still sore. I had to make a decision as to what I was going to do.

"I spoke with the guys and decided the best thing was to rest and try and make sure I can actually let my body kind of adjust to the surface."

Murray said that with his travelling physio on hand, he feels he has a chance to be first before the Cincinnati start.

"I'll be able to get as much treatment as possible. I wasn't able to to do anything to adjust to the surface (from Olympic grass) and get used to the movement at all.

"I'll be able to do that and give it a few days and see how it feels.

"The hard courts, for me anyway, are the hardest on my body. It always takes me a bit of time to get used to playing on them again. I hope it doesn't affect the next few weeks too much.

"Now I have to take a couple days off without playing, so this (injury) may have set me back slightly."