Andre Agassi has labelled Roger Federer 'unique' and believes the Swiss ace is one of a kind in the way he approaches the game on-court and off it.

The 36-year-old dominated the sport in the early part of the current decade before the emergence of Rafael Nadal and then a little after Novak Djokovic, who were the only two players that actually prevented Federer from amassing more than the record 19 men's singles Grand Slam titles he currently holds.

Federer has been labelled the Greatest of All Time (GOAT) on a number of occasions, but it is difficult to compare between different eras with the likes of Rod Laver also considered one of the greatest to step on the court, especially as he is the only one to have completed the calendar Grand Slam on two occasions.

Agassi believes the Swiss ace's style of play is unique and something no other player can match. The American feels Federer makes his game look easy and does not require the physical exertion other players need.

Federer was struggling for form in recent seasons and had not won a Grand Slam since 2012 prior to his resurgence in 2017. He missed the last six months of the 2016 season due to injury, when questions were raised about his future in the game.

The 19-time Grand Slam champion, however, returned and silenced his critics with a new aggressive brand of tennis. He won seven titles this season, including two major titles, and is back to world number two in the rankings after starting the year at 17.

"Federer is unique. In everything: greatness, precision, easiness. He plays tennis in a different way than others," Agassi said, as quoted by Tennis World USA.

"When I say easiness, don't misunderstand me: it's not easy. But it seems Federer controls everything, has a solution for any issue. With so many options, he has the power to avoid the physical intimidation that many current players use.

"He knows that he can play elegantly, smartly, handle his efforts, take his time to get his injuries healed, learn new things and keep investing in his progresses. We can't deny that Federer will mark the sport forever," Djokovic's coach added.

Roger Federer
Roger Federer took his Grand Slam tally to 19 in 2017 following his wins in Australia and London Getty