Both Federer and Nadal have had career resurgences in 2017, winning a combined six titles, including two Grand Slams each as the duo returned to the top two of the ATP tennis rankings.
Uncle Toni though, somewhat surprisingly revealed that he believes Federer, who boasts 19 Grand Slam titles, is the GOAT rather than Nadal who has 16 Grand Slam titles and is the current world number one.
However, he believes that if the Spaniard went on to win even more Grand Slams following Federer's potential retirement, opinions might change on the matter.
"Federer is the best player in history," Toni Nadal told Cadena SER Radio, as quoted on Tennis World USA. "I know only a few sportsmen who dominated the sport as much as Roger did in tennis."
"Rafa is playing at an exceptional level, just look at this year's results, and I am totally sure he will be among best players ever.
"If Federer retires within a few years and Rafa keeps winning Grand Slams, then we will speak about GOAT question but at the moment I think it's Roger."
Federer's status as the GOAT was no doubt, strengthened after his fourth win in a row over Nadal this year during the final of the Shanghai Masters.
Nadal was on a 15-match unbeaten run until he squared off against the Swiss ace who was simply too good for the 31-year-old, winning in straight sets.
"Roger is at a fantastic level," Toni added. "He made a change in his game that seems to be very smart to me. It makes him more aggressive than a few seasons ago."
"Now it's much tougher to play against him, especially on hard-courts where I think he is the best player. Obviously he is the big favourite at the ATP Finals in London."