(CNN) -- Olympic gold medalist Andy Murray was forced to pull out of the Toronto Masters Thursday with a knee injury.
Murray flew into Canada after his gold medal triumph at Wimbledon Sunday over Roger Federer and duly swept aside Italian Flavio Cipolla in his first match.
But he withdrew before his last 16 clash with home hope Milos Raonic.
"It's unfortunate. I think it would have been a fun match," Murray told the official ATP website.
"I hope he has a good tournament. Be great for him to go deep in this tournament here for the first time."
Britain's Murray had received treatment on court during his Wednesday win over Cipolla and decided not to risk it ahead of the final grand slam of the season at the U.S. Open later this month.
"It was a bit sore yesterday, then I had some treatment after the match. It felt a bit better, and then came in today, I saw the physios, they did some work on it, and it's still a bit sore."
Canada's Raonic spoke with Murray and wished him to "get healthy quick" before adding: "It's my first quarterfinal in a Masters and to be at home is pretty special. I guess there is a give and take with it."
Serbia's Novak Djokovic, the top seed, was facing American Sam Querrey for a place in the quarterfinals later Thursday.
Meanwhile, Spain's Rafael Nadal has also withdrawn from next week's Cincinnati Masters event due to due to the left knee soreness that has sidelined him since Wimbledon and forced him to miss the Olympic tennis event.