The participation of Roger Federer in next month's Montreal Masters remains uncertain, depending on when his heavily pregnant wife gives birth in Switzerland.

With Mirka Vavrinec's due date top secret, the summer schedule of the No 1 and 15-time Grand Slam champion is up in the air. Reports indicate that if the child is not born before the end of July, then Federer will delay any travel to North America from his lakeside base near Zurich.