Montreal, July 24 (DPA) 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 Aug 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.