Rod Laver, Roger Federer, Rafael Nadal
Apr 2, 2017; Key Biscayne, FL, USA; Rafael Nadal of Spain (L) and Roger Federer of Switzerland (R) hold the finalist and Butch Buchholz trophy, respectively, after their match in the men's singles championship of the 2017 Miami Open at Crandon Park Tennis Center. Federer won 6-3, 6-4. USA TODAY Sports / Geoff Burke

Former World No. 1 Marat Safin is of the opinion that Rafael Nadal's career is more impressive than that of Roger Federer simply because of how much harder the Spaniard worked to win 16 Grand Slams. In 2017, Nadal and Federer split the four Grand Slams with two wins apiece, to further their storied careers.

While Federer has enjoyed a more well-rounded game and a near flawless service game, Nadal has made a career out of prevailing over and tiring out opponents courtesy of his stamina and endurance. Safin believes Nadal has been forced to fight for everything, while Federer's career is built upon outstanding talent.

"Nadal is more impressive than Federer. The latter had everything to be successful, while Nadal is a true wrestler and worker. He’s sweating more and does not get tired. For Federer it’s all easier, though Nadal gives the impression that tennis is a simple thing for him," Safin told Live Tennis in an interview, via Metro.

In October, Federer made history by defeating Nadal for a fifth consecutive occasion in the finals of the 2017 Shanghai Masters. Though Nadal has had the better of Federer in their illustrious rivalry, the Swiss Master has dominated the Spaniard in recent years.

Rafael Nadal has had to work harder, says Marat Safin

"Federer and Nadal have been there for a long time. If we look at the to-10, nothing has changed since I retired in 2009. But that will change. Those in their 30s will soon give their place to young people, who are faster and will improve with time," the Russian added.

Marat Safin, who won the 2000 US Open and 2005 Australian Open during the course of his career, is thoroughly impressed by the game of rising German star Alexander Zverev.

"Alexander Zverev has so much potential, but he is still too young. In a year or two he will be a different player. You still see yourself as a junior, but he is no longer a junior, he has to believe in himself and keep working. ‘Today’s tennis is more physical and fast. Players have less time to think and it’s a good thing," added Safin.

At 31, Rafael Nadal recently became the oldest player in ATP rankings history to finish a season at World No. 1. Nadal was presented with the trophy at the Nitto ATP Finals in London. Nadal and Federer will enter the 2018 Australian Open as the co-favourites despite the imminent returns of Novak Djokovic and Andy Murray.