Roger Federer has been forced to withdraw from the 2017 Western & Southern Open in Cincinnati, Ohio, due to a back injury.
The 19-time Grand Slam winner announced the news Monday—the first day of the tournament—that he picked up a problem as he was runner-up in last week's Rogers Cup in Montreal, per the ATP World Tour: "I am very sorry to pull out of the Western & Southern Open as I always enjoy playing here. Cincinnati has some of the best fans in the world and I am sorry I will miss them. Unfortunately, I tweaked my back in Montreal and I need to rest this week."
The Swiss legend was beaten in Sunday's Canada final by 20-year-old Alexander Zverev of Germany.
Federer, 36, joins fellow top players Stan Wawrinka, Kei Nishikori, Andy Murray, Novak Djokovic and Marin Cillic in withdrawing from this year's Western & Southern Open.
His non-participation means Rafael Nadal is guaranteed to return to world No. 1 on Monday, Aug. 21, for the first time since 2014, per the ATP World Tour.
Federer and Nadal, 31, have shared the three Grand Slam titles of 2017 so far—the Swiss winning the Australian Open and Wimbledon, the Spaniard the French Open—and both will hope to be fit and firing for the U.S. Open, which begins later this month.