Federer, Nadal firm for No.1 after Murray setback

World No.1 Andy Murray has withdrawn from next week's Canadian Open in Montreal as he continues to recover from a hip injury, Tennis Canada has announced.

Murray has been in rehabilitation from the problem that ruined his Wimbledon campaign, but the tournament in Canada comes too soon.

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"I am sad to be missing the tournament in Montreal because I have many great memories from my time in Canada," he said on the tournament's official website.

"I am doing everything I can to return as quickly as possible."

Murray was joined on the sidelines of the pre-US Open warm-up by Croatian world No.6 Marin Cilic. Former world No.1 and 2009 finalist Maria Sharapova also announced her withdrawal from the women's event on Thursday.

"We would have liked for Andy to be able to defend his title that he won here in 2015, but we wish him a very speedy recovery and to Marin Cilic as well following his great run at Wimbledon," said tournament director Eugene Lapierre.

The top two seeds at next week's event will be Rafael Nadal and Roger Federer, with young guns Dominic Thiem of Austria and German Alexander Zverev rounding out the top four.

Murray's absence means he's almost certain to lose his No.1 ranking to either Nadal or Federer.

Murray has spent the past 39 weeks as No. 1, but needs to win virtually every big title for the rest of the year to retain it, something that is now virtually impossible.

As we head into the American hard court season, Nadal (7465) trails Murray (7750) by only 285 points and leads Federer (6545) by 920 points.

Therefore the No.1 ranking will likely come down to who performs better in Canada and Cincinatti.

The thought of Federer or Nadal back at No.1 was unfathomable at the start of the year, with Nadal ranked No.9 and Federer 16th following injury-plagued 2016 seasons.

But 2017 has seen the pair experience an incredible resurgence, with the Swiss great winning the Australian Open and Wimbledon, while the Spaniard won his 10th French Open crown.

Outside of the majors, Nadal also won titles in Monte Carlo, Barcelona and Madrid, while Federer was victorious at Indian Wells and Halle.