Andre Agassi believes that Rafael Nadal is tennis' greatest ever player, rather than Roger Federer.
Despite leading the all-time Grand Slam title list, Federer should not be considered the best because Nadal has faced tougher challenges in a 'golden age' for the sport according to Agassi.
The retired American star won eight majors himself before he called it a day in 2006. It was Federer who denied him a dream ninth win at his last final appearance at the US Open in 2005, meanwhile the Spaniard beat him in round two of a farewell Wimbledon trip.
Out of the two, the former world no.1 rates the currently best ranked player as the superior man.
In an interview with a Singapore newspaper, the 44-year-old is quoted as saying on ESPN.com: "I'd put Nadal No. 1, Federer No. 2.
"It's just remarkable to me what he has done, and he has done it all during Federer's prime.
"Nadal had to deal with Federer, (Novak) Djokovic, (Andy) Murray in the golden age of tennis. He has done what he has done and he's not done yet."
The two between them have an astonishing 30 Grand Slam singles titles
Federer surpassed Pete Sampras' record of 14 in 2009 when he beat Andy Roddick at Wimbledon, in what turned out to be the longest final in the history of the game.
The Swiss star has since extended his lead with another three success, however, the 32-year-old's last triumph was at SW19 in 2012 against home favourite Andy Murray.
Many believe that the 26-year-old Nadal can usurp his rival in the all-time chart. He currently has 13 to his name, thanks largely to his eight wins at the French Open.
Dubbed the 'King of Clay', he has only ever lost once at Roland Garros - a shock fourth-round loss to eventual runner-up Robin Soderling in 2009 - and now he has the chance to draw level with Sampras on the list with a ninth Paris gong.
The two great athletes have met on the court 33 times. It's Nadal who leads their head-to-head record with 23 wins, he has also won their last five encounters.
They were due to meet at the ongoing Madrid Open as the French Open approaches. However, Federer was forced to pull-out a few days into the tournament after wife Mirka gave both the couples second set of twins.
Nadal is looking for fourth title in front of his home fans,and the absence of his rival makes that task considerably easier.
Agassi held off retirement long enough to face the duo. Federer beat him in all of their last eight matches in a total of 11. Nadal won both times as a teenager, one in a final at Canada.
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