Rafael Nadal believes Carlos Alcaraz can be 'practically unstoppable' after he lost to the 19-year-old at the Madrid Masters.
It was their fourth meeting, with Nadal winning the previous three, but Alcaraz downed the 21-time Grand Slam champion to become the first ever teenager to defeat him.
After a blistering start, Alcaraz had to overcome an ankle injury in the second set, but Nadal was still unable to contain the youngster.
Alcaraz will now face world number one Novak Djokovic in a blockbuster semi-final.
"The first thing is to congratulate him," Nadal said of Alcaraz. "First of all, happy for him, he has been better than me in various facets of the game and I need to improve these days.
"It is accepted naturally and calmly, with the certainty that there is a path to follow and arrive with real options to generate opportunities.
"It is an easy defeat to digest, we knew what we were coming here for and we have to congratulate Carlos, he is playing well and I wish him the best for the rest of the tournament."
Asked if he feels Carlos Alcaraz can beat Novak Djokovic yet, Rafael Nadal said: "I haven't seen Novak play this week.
"I don't know what will happen: one of the best players in history is playing against a youngster at a very high level.
"Carlos can win perfectly, I don't see any reason why he can't win. It's true that he can't have a slump like the one in the second set.
"He plays a lot with moods, when his adrenaline goes up he's practically unstoppable. Then, of course, he makes mistakes because he plays with a lot of risk.
"I think he has the level to beat anyone in the world, without a doubt."
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