Toni Nadal thinks nephew Rafa Nadal, Roger Federer and Novak Djokovic will find it hard to rack up more major titles in the coming years.
The trio are consistently hailed as the best three players to ever play men's tennis and have dominated the Grand Slam scene as a collective since the late 2000s.
But speaking at a press conference detailing next summer's ATP 250 event in Majorca, Toni said he thought that situation might be at an end.
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Asked whether 21 slams would be enough to win the major GOAT race, he said: "I have no idea. I wish I did.
"Djokovic is in theory the favourite to win Wimbledon, at Roland Garros I hope it will be Rafael and the US Open I don't know.
"It [21] may or may not be enough. The reality is that it is increasingly difficult to win a Grand Slam because of their ages and because of the players who come from below [the next gen]."
Toni was also candid about his nephew's physical state, declaring his surprise at how long Nadal has been able to play for given his congenital foot issue - whilst warning it will impact his life at some point in the future.
He said: "The specialist who saw him in 2005 told us that it would be very difficult for him to do sport at the highest level, but Rafael has been defying that in the best possible way, because he has been able to face up to a difficult situation.
"He looked like he was going to have a short career, but everything has turned out much better than we expected. He will have a solution when he finishes his career, but not while he is playing.
"Depending on the operation that is done, he will not be able to play at a high level anymore, that is why it cannot be done now."
Toni also gave another take on the GOAT debate, but revealed that he is not the best man to judge it given his family connections.
He said: "There are different measures to determine who is number one [of all time].
"In any case, my opinion is not valid because he [Nadal] is my nephew, and if I considered that someone else is the best, I would not say so.
"Federer is a guy who has managed to transcend his sport.
"But apart from that he has achieved maximum efficiency with great elegance, and you can't ask for more than that.
"As for Rafael, obviously, he has also had to change things, but I think that is what all those who stay at the top for a long time do. It's impossible to stay on top if you are not constantly reconfiguring yourself.
"He [Rafa] has changed, like Federer. If you can't run as much you know you have to shorten the points. The level of Rafael's game between 2008 and 2010 was very high. Today he has a little less physicality, as is to be expected, but his game is more complete, he now serves much better."
Despite all that Nadal has achieved, Toni said that he would "never say of a family member that he is a genius".
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