Toronto, Aug 10 (IANS) Olympic gold medallist Andy Murray withdrew from the Rogers Cup due to a knee injury, joining the growing list of top players absent from Canada's annual tennis event due to injury, fatigue or first-round eliminations.

Murray, ranked fourth in the world, announced his withdrawal from the tournament Thursday, as the fourth day of the 2012 Rogers Cup held in Canada's largest city was washed out by rain throughout the day, reports Xinhua.

Murray said he made the decision Thursday morning, due to concerns about further damage to a sore left knee, which forced a medical timeout during his opening match Wednesday. Murray won 6-1, 6-3 against qualifier Flavio Cipolla of Italy.

The tired-looking Scot blamed the lack of time to train for hard courts, which are hardest on his body, after the grass courts at Wimbledon, where Murray defeated Roger Federer last Sunday to clinch the Olympic title.

Normally when I move on to hard courts, you know, you have ten days or so practising and you feel things like this, but you can work round it by doing the right training and whatnot; whereas I don't want to go full out and possibly do any more damage (to the left knee), said Murray.

That was why I decided not to play.

Murray said he will undergo physiotherapy for his knee and train on the hard courts over the next few days. The US Open, the last Grand Slam event, is played on hard courts and will be held in New York from Aug 27-Sep 9.