Rafael Nadal's uncle fears Jannik Sinner is 'practically unstoppable'

World No. 1 Jannik Sinner got his first taste of grand slam glory at the 2024 Australian Open and grew in confidence the rest of the year, capturing five more titles, including the 2024 U.S. Open.

With two major titles under his belt, the 23-year-old will be hard to stop in 2025 if he keeps at his current pace. That is the opinion of Toni Nadal, the uncle and former coach of Rafael Nadal.

In a column published on "El Pais," Nadal wrote that Sinner's ascension could be an ominous sign for other players on the Tour, including World No. 3 Carlos Alcaraz.

"Today, he has become a player who is practically unstoppable for the vast majority of his opponents," Nadal wrote of Sinner. "He is capable of delivering each of his strokes with great speed and with very few unforced errors. Overcoming him from the back of the court is almost impossible...I must say that I still enjoy Alcaraz's game more — I like him even more — but I must also admit and fear that the current leader's notable improvement, especially on a mental level, will make things really difficult for him. The rivalry is definitely on."

Nadal further noted that U.S. star Taylor Fritz made the mistake of playing "very fast rallies" from the back of the court against Sinner in the U.S. Open final — a recipe for disaster against the Italian. Nadal felt Fritz was trying to surprise Sinner with winners from the baseline only to find out that making the World No. 1 miss on those rallies is "practically impossible" for any player on the Tour.

While Sinner's style is more suited to the hard courts, he made the semifinal at Roland Garros and the quarterfinal at Wimbledon this year, showing his ability to adapt to other surfaces. As such, Nadal feels Sinner could become an even more dangerous player if he starts winning on clay or grass courts.

As Nadal said, the Sinner vs. Alcaraz rivalry "is definitely on" and could retake center stage in 2025, a year after they split the four slams among them . Many feel the two rising stars could dominate tennis over the next decade, much like the famed Big 3 did for the last two decades.