Novak Djokovic returns to tennis for the first time since Wimbledon as the Serb begins his bid for a third straight title when the Montreal Masters begins on Monday.
Djokovic has not played since losing the Wimbledon final to Andy Murray, the second seed who will also be testing himself for the first time in a month since making history with his title at the All England Club.
Missing from the field will be two-time champion Roger Federer, the world number five, with the Swiss apparently unable to overcome the back spasms which bothered him in recent weeks as he played for the first time in years at clay events in Hamburg and Gstaad.
ATP number five Federer gave no precise indication of why he will not make the trip to start his pre-US Open campaign, saying only: "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."
Also pulling out was wild card Gael Monfils, who had the misfortune to injure his ankle while training at the tournament site in Canada.
American Mardy Fish, never the same since his heart-scare incident nearly 18 months ago, withdrew for "personal reasons".
Serb Viktor Troicki and Croatian Marin Cilic, both under clouds for alleged violations of the tennis anti-doping policy, are not included in the field for the first major tune-up prior to the US Open which begins August 26.
Troicki has been banned for 18 months for failing to provide a blood sample to drug testers, but he says the testing personnel told him he didn't have to and he plans to appeal.
Murray and fourth seed Rafael Nadal both got in hits in Montreal with Frenchman Richard Gasquet, with Murray building for the first grand slam title defence of his career in New York where he finally made his breakthrough at a major at the US Open 11 months ago.
"I think I persevered, that's really been it, the story of my career. I've had lots of tough losses, but the one thing I would say is I think every year I always improved a little bit," the Scot said of his ever more impressive resume.
Murray lifted the Montreal honours in 2009 and 2010 but lost in the third round a year ago to Canadian Milos Raonic.
The top eight seeds receive byes into the second round, with Djokovic playing the winner of the first-round match between Australian Bernard Tomic and Germany's Florian Mayer.
Murray will line up against either Grigor Dimitrov or Marcel Granollers, who reached won the claycourt title in Kitzbuehel, Austria, on Saturday.
Spain's David Ferrer is seeded third, with Czech Tomas Berdych fifth behind Nadal. Argentina's Juan Martin del Potro is sixth, with Gasquet seventh and Switzerland's Stanislas Wawrinka eighth.