Roger Federer pulls out of Cincinnati; Rafael Nadal to retake No. 1

Roger Federer has pulled out of this week's Western & Southern Open in Cincinnati with a back injury, meaning Rafael Nadal will retake the No. 1 ranking on Aug. 21.

The final Masters 1000 event before the U.S. Open made the announcement on Twitter on Monday.

The withdrawal comes just a day after the 36-year-old was upset by Alexander Zverev, 6-3, 6-4, in the Montreal final for just his third loss of 2017. (It was also the first time in 38 matches this year that he's lost in straight sets.)

"Unfortunately, I tweaked my back in Montreal and I need to rest this week," he said.

The 19-time Grand Slam champion, who isn't scheduled to play again until the U.S. Open kicks off on Aug. 28, joins a long list of ATP stars who won't be in Ohio this week. Novak Djokovic and Stan Wawrinka are out for the season, current No. 1 Andy Murray is recovering from a hip injury and Marin Cilic is out with an abductor injury. World No. 9 Kei Nishikori has also pulled out with a right wrist injury.

Of the Top 6 players in the world, only Nadal is in the Western & Southern Open draw. The Spaniard is just 195 points behind the Scot, and Murray—last year's runner-up in Cincinnati—had 700 points to defend this week. Federer, ranked third, is 605 points behind Murray and 410 points behind Nadal. Had Federer played this week, he would have had a shot to become the new No. 1.

Nadal, who was beaten by Canadian teenager Denis Shapovalov in Montreal last week, will return to the top of the rankings for the first time since the week of June 23, 2014. (He first reached No. 1 in 2008.)  He said he was especially disappointed by that loss because of the added "opportunity I had here to come back to No. 1." That, as it turns out, has taken care of itself.

The world No. 2 and top seed in Cincinnati will take on veteran Richard Gasquet in his opening match.

(Reporting by Brad Kallet and Kamakshi Tandon.)

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