Roger Federer on Friday withdrew from next week’s Montreal Masters only hours before the draw ceremony with his recent back problems apparently still giving him trouble.

The Swiss, ranked fifth, gave no precise indication in a statement of why he will not make the trip to start his pre-US Open campaign.

'I am disappointed not to be playing in Montreal next week. It is a great tournament with amazing fans. I look forward to competing there in the future,' he said.

The 31-year-old who celebrates a birthday next Thursday, was bothered by back spasms as he played on clay last month in Hamburg and Gstaad. The Swiss won the Canadian title in 2004 and 2006.

Rivals Novak Djokovic, Andy Murray and Rafael Nadal — who has now played since losing in the Wimbledon first round and resting his knees — are already in Canada.

Officials also announced that Serb Viktor Troicki and Croatian Marin Cilic have withdrawn. Both are suspected of anti-doping infractions. Ivan Dodig of Croatia and Spaniard Pablo Andujar replace them in the main draw.

Withdrawing earlier were French wild card Gael Monfils after injuring his ankle during training, and American Mardy Fish, who pulled out for 'personal reasons.'