John McEnroe has issued a warning over Carlos Alcaraz’s height, with the Spanish star regularly up against opponents much taller than him.

Standing at slightly under 6ft, the reigning Wimbledon and French Open champion is proving to be an outlier against his towering rivals, with McEnroe among those to stand up and take notice.

The American has warned Alcaraz that he will be driven “absolutely nuts” as he continues to play against taller opponents with a stronger serve. Despite his ferocious nature on the court, McEnroe fears that the 21-year-old will get worn down physically.

“This guy is the greatest talent I’ve seen in the last 20 years and he is the best to watch,” said McEnroe on the Served podcast.

“You look a the guys (his rivals) and they are all so tall… do they have the explosive speed of Alcaraz? No, but I worry that because he is only six feet and a half an inch tall, they are going to drive him absolutely nuts.

“He’s going to play these guys that serve out of a mountain and (Alcaraz) will get frustrated. This is what happened at the end of last year and it happened on a handful of occasions.

“I hope that I’m wrong about Alcaraz and that he is not going to be able to keep this up. I still think he is going to get 10 of them (Grand Slams), which would be unbelievable!”

It is not the first time that McEnroe has heralded Alcaraz in such a way, telling Tennis365 earlier this year that he has eclipsed the likes of Roger Federer, Rafael Nadal and Novak Djokovic when they were his age.

“Alcaraz is my favourite player to watch right now. He can do everything and he does it all so well. It seems almost impossible that he would be that positive every week, that he can win as often as he does at that age,” McEnroe said.

“The smile, everything about him, it’s hard to believe he doesn’t get frustrated in a sport that is as frustrating as tennis is. Trust me, I know what it’s like to get frustrated in tennis!

“Doing what he did in Paris, playing as amazing as he did at Wimbledon, getting to the gold medal match Olympics and playing an amazing match against Novak.

“He’s already better than Federer, Nadal and Djokovic at 21. I’ve said this before and I’ll say it again for the record. Carlos Alcaraz is my favourite player to watch.”

So far Alcaraz has not stopped his height from becoming one of tennis’ biggest threats, picking up four Grand Slam titles and reaching world No. 1, but McEnroe has a warning to be heeded.