With a head-to-head record favoring Rafael Nadal 23-10 against Roger Federer, retired American tennis star Andy Roddick says the debate as to the greatest-ever is equally one-sided.

In favor of Federer.

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The Australian edition of the International Business Times reported that Roddick, the last U.S. player to be ranked No. 1 in the world, said Federer's edge in Grand Slams still gives him the edge over Nadal in the growing debate.

"For me, Roger Federer is still ahead in the greatest-ever debate, with Rafael Nadal second," Roddick told the International Business Times.

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He said the head-to-head disparity takes a back seat to the overall résumés of both players. Federer owns 17 Grand Slam titles; Nadal has 14.

"In its most simplistic state, while Roger has more major titles than Rafa, Roger is the greater player - major championships are what define our sport," said Roddick, who retired after the U.S. Open in 2012.

Roddick pointed to former No. 1 Pete Sampras' record against South African Wayne Ferreira as an example of putting too much stock into head-to-head rivalries. Sampras had a 7-6 record against Ferreira, but no one every talks about Ferreira as one of Sampras' chief rivals.

Sampas meanwhile, had a 20-14 record against main rival Andre Agassi.

Federer passed Nadal in the rankings, thanks in large part to Nadal's inability to stay healthy. The Spaniard suffered back, knee, and wrist injuries that derailed his 2014 season but did include another French Open title. Federer, meanwhile, made it to the U.S. Open final and won four non-slam titles this season.

He has an outside chance of overtaking No. 1 Novak Djokovic at the ATP World Tour Finals in London later this month while Nadal was forced to skip the ATP finals because he is recovering from appendectomy surgery.

What should count more in determining the greatest tennis player ever - head-to-head matches or overall championship titles? Comment below or tell us @SportsWN.