Montreal, Aug 4 (AFP) Defending champion Rafael Nadal heads the field for the ATP Montreal Masters that starts on Monday with Novak Djokovic and Roger Federer opting out of the key US Open tuneup.

With Djokovic and Federer putting a return to action on hold after their dramatic Wimbledon final, 33-year-old Nadal will be seeking to retain the title he earned last year in Toronto, when he beat rising star Stefanos Tsitsipas in the final.

The Greek is back, taking the fourth seeding behind a pair of fellow young guns in number two Dominic Thiem of Austria and Germany's Alexander Zverev, seeded third.

Federer and Djokovic aren't scheduled to resurface until the Cincinnati Masters starts on August 12, giving them one tournament prior to the August 26 start of the US Open at Flushing Meadows, the final Grand slam of the year.

Federer has been training on hardcourt at home in Switzerland after falling to Djokovic in a dramatic five-set final at the All England Club three weeks ago, in which the Swiss great held two match points.

Djokovic has been pictured relaxing at various European beach resorts with his family prior to picking up the racquet once again.

Nadal, meanwhile, is pacing himself after another season marred by injury, insisting despite the pleas and inducements of Cincinnati officials that he won't decide whether to play there until he sees how he feels after Montreal.

"Depending on what happens in Montreal, I'll take a decision on Cincinnati," he said.

"Cincinnati is still an option. But I want to arrive well prepared and ready for the US Open, the last major of the season."

Nadal could face a challenge in the second round after a bye, with a possible match against Australian Alex de Minaur -- winner of the Atlanta title last weekend.

Second seed Thiem has purposefully left it late for the hardcourts, preferring to stay as long as possible on European clay by entering both Hamburg and Kitzbuehel.

Thiem, beaten by Nadal in the last two Roland Garros finals, has a special goal driving him when he lands in francophile Canada.

"I've never won a match in Canada, I'd like to change that." he said.

"I'm just hoping to play well.

"Canada is a big goal - I'm really hoping to get a win there."

Thiem will open his campaign against either Canadian Denis Shapovalov or Frenchman Pierre-Hugues Herbert.

Third seed Zverev, who won the title here two years ago with a win over Federer in the final, will open against either Briton Cameron Norrie or Hungarian Martin Fucsovic.

Tsitsipas will bid to better his 2018 finals showing but must first get past either home-grown Milos Raonic, the 2013 finalist, or American Taylor Fritz, runner-up to de Minaur in Atlanta. AFP

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