Montreal - 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 number one 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.

Despite what have to be exquisitely timed plans for the baby to be born between Wimbledon and the August 9 start in Canada, nothing can be certain at this point.

The Swiss also faces a timing crush with the Cincinnati Masters starting the day after Montreal ends, with those pair of high-profile events the only two in Federer's diary before the start of the US Open in late August.

Montreal officials are said to be willing to give Federer a late start date on Wednesday, August 12 should he request it.

Perfect symmetry would indicate that the babe be born on August 8, his own 28th birthday. Canadian media have quoted the Montreal tournament boss as saying he is not actually expecting Federer to front up.

Even in the potential absence of Federer, Montreal will not be lacking in buzz, with Rafael Nadal due to return to the courts more than two months off the ATP resting tendinitis in his knees which kept him from Wimbledon.(dpa)