Ahead of the Rogers Cup in Montreal, Roger Federer does not think he will be able to keep up what has been an overachieving year so far.

The Swiss ace returned from a six-month layoff earlier this year to win the Australian Open in what was his first Grand Slam victory since 2012.

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Federer then won titles in Indian Wells, Miami and Halle before winning an unprecedented eighth Wimbledon title after a dominant straight set 6-3, 6-1, 6-4 victory over Marin Cilic last month.

Federer's year has defied belief as the 36-year-old currently boasts five titles and could end 2017 as the world number one for the first time since October 2012.

With the hard-court campaign commencing this week ahead of the US Open later this month, Federer spoke of his longevity and how playing for a long time was one of his early goals.

"I always had longevity written all over my career that when I became world number one in 2004, my goal was to hopefully play for long," Federer said in a pre-tournament interview in Montreal. "I had the chance to play against Agassi who played until 35 or 36 and I really appreciated the fact that he stuck around and I thought if I could do the same, it would make me very happy."

The 19-time Grand Slam winner also compared his two major wins of the year before stating that it was not realistic to think the results so far will continue.

"It's been a magical year and I think because everything happened so quickly, and all the matches were three sets in Wimbledon, it didn't feel like it was the epic battle that I had in Australia so it had a totally different taste," he added.

"Maybe even a deeper happiness winning Wimbledon and writing history there at the tournament, it means so much to me. God, what a six months it's been, I hope I can keep it up even though I don't think so, we'll see what happens.

"It was just too good. It's just not realistic to think that way but I'll try everything to keep on playing good tennis for the rest of the season. Even though I should be feeling better the second part of the season, the first part has been so good that it's going to be really hard to top."

Federer will play his first match in the Rogers Cup round of 32 as he takes on Canada's Peter Polansky on Wednesday (9 August).