Australian Nick Kyrgios "doesn't understand" what it takes to be a Grand Slam winner, says three-time Wimbledon champion John McEnroe.
Kyrgios, 21, lost 7-5 6-1 6-4 to British number one Andy Murray in Monday's much-anticipated last-16 tie.
"I hope he sees the writing on the wall before this gets chronic and irreparable," the American seven-time Grand Slam champion told BBC Sport.
"It's not just the mental side, he needs to work harder at his game."
Kyrgios is the youngest player in the world top 20, but his success has been marred by questions about his attitude.
He rose to fame by beating Rafael Nadal at Wimbledon but has been involved in a number of controversies, such as making remarks about Stan Wawrinka's girlfriend during a match last year, resulting in a suspended 28-day ban from the Association of Tour Professionals.
"He doesn't understand what it takes to be someone who wins Grand Slams at this level and that is unfortunate," McEnroe added.
I'm a bit soft - Kyrgios
Kyrgios did not react to McEnroe's criticism, but asked if he felt he was applying himself the best he could, he replied: "No."
He added: "When things get tough, I'm just a little bit soft.
"I've got experience, but it ultimately comes down to just laying it all out there and competing for a long time. I didn't do that today at all.
"At times, like I've previously said, I don't love the sport. But I don't really know what else to do without it. I know that I have the talent to do good things.
"I woke up this morning and played computer games. Is that the greatest preparation? I don't know, but it was fun.
"Every time I come here, I lose to good players. But it's just disappointing. I don't know. I just want to do better."
'Kyrgios must look in the mirror'
Kyrgios made 19 unforced errors in the fourth-round match against Murray - three times more than the Scot - and did not earn a break point.
The second set lasted just 26 minutes after a tight first set, which Murray claimed by breaking Kyrgios in the 12th game.
"Kyrgios has to look in the mirror if he wants to become a top player and win Slams," said McEnroe, who was involved in a number of heated exchanges with umpires during his career.
"I still think he will win Slams but not how he did it there. You can't give away points and games against someone as good and focused as Murray. Inexplicable. He's got to ask himself how badly he wants to become the best player in the world."
Shortly before the match, Kyrgios was pictured courtside as fellow Australian Lleyton Hewitt competed in the doubles competition.
McEnroe said: "What kind of preparation is that? Two hours before you're out on Centre Court you're watching a doubles match! I know you need to keep nerves down, but come on."
Kyrgios denied that watching compatriot Hewitt's match before taking on Murray had hindered his performance.
"Whether I was in the locker room sitting down or sitting down next to the court, I don't think really made a difference," he said.
I understand he does not love tennis - Cash
Compatriot Pat Cash described Kyrgios as a "different sort of kid" but also said he is "definitely talented".
Cash, the 1987 Wimbledon champion, added: "I think that is what frustrates a lot of Australians. To see that much talent, you want it to be utilised better.
"I just don't think he is that type of kid. He is getting better. He is doing his best to not get in as much trouble this year, though he still has a few fines.
"Nick says he doesn't really love tennis and I understand that. I didn't love tennis, I was just good at it. Andre Agassi said the same thing."