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.
