John McEnroe believes there is one reason why Nick Kyrgios cannot go far in the Grand Slams so far. The American said: "I think he’s had a difficult time getting himself in the type of condition where he could go the distance.
He’s talked about it. He doesn’t train hard. I think he’s training harder. You have to take it to the stratospheric level. Physical part is a big part. Look how calm Roger Federer keeps himself in think situation.
That’s a talent, you save energy, don’t waste energy. Rafa Nadal seems to have boundless energy. Guess what, he’s training as hard or harder than anyone. Novak Djokovic has a combination of what the two have. On the court, the stress that can cause fatigue.
That’s a thing that a lot of kids find out when they’re faced with difficult situations. All of a sudden they can’t figure out why they’re tired. They have to understand the mental part of it. This is a big part of what you need to do in order to get over the hump.
These young players are making some pretty good progress. Some guys have stalled. Tsitsipas, he struggled recently. He’s had some trouble dealing with people close to his own age. He doesn’t really understand, I don’t think, what he needs to do on a quicker hard court or grass court.
Depends on each person. Some of these guys, Felix Auger-Aliassime from Canada, Shapovalov, if you look at them physically, they’re pretty darn mature. One is 20, the other is 19. They both look like they’re 25. They look ready to go.
Last year Felix had some issues with his heart. It seems to be behind him, which is great. You think that he’d be capable of doing it. Denis physically, I think in his case could be more mental, with the strength you need mentally to deal with these guys.
They’re making progress. It’s the guys mid to late 20s, 30s that have had a tougher time dealing with the mental part of it, understanding what it takes to get over the hump with the top guys. That’s what separates them."