Roger Federer and Rafael Nadal
Roger Federer and Rafael Nadal at Roland Garros 2005.Julian Finney/Getty Images

Rafael Nadal is one of the only two strongest sportsmen in tennis, according to Roger Federer's former coach Jose Higueras.

Jose Higueras coached Roger Federer in 2008 and he says Rafael Nadal and Bjorn Borg are the only two tennis stars who have a strong mentality. That means Federer and Novak Djokovic are not as strong as Nadal mentally, according to Jose Higueras.

"When I saw him so young, he did not stand out for his technique but for his mental strength," said Jose Higueras. "I only saw it in Rafael Nadal. They are the strongest two tennis players, well I would say sportsmen in general, mentally," he added.

Not that many would agree because Roger Federer and Novak Djokovic are the two tennis stars from the current lot. They have collectively won 35 Grand Slam titles, with the Swiss tennis legend winning 20 of them and Djokovic winning the remaining 15.

Rafael Nadal has won 17 Grand Slam titles and the three tennis players are in the top three in the list of most number of Grand Slam titles won by Men's Singles in an open era. Jose Higueras also spoke about the rivalry between Roger Federer and Rafael Nadal, which started in the early 2000s and has still continued even till date.

"I am sure I will not see another rivalry like this and I do not know if we will see again two players like Roger and Rafa who influence so much the rest of tennis players for their game style," Jose Higueras continued.

"Champions would have been champions in any era, what marks a champion is usually the character and not so much the tennis quality, and the best thing about this kind of players was the ability to adapt."

The rivalry between Roger Federer and Rafael Nadal is only inside the tennis court and not away from it.