Rod Laver says Nick Kyrgios needs to stop trying to be an entertainer and take a discipline pill in order to maximise his undoubted potential.
Kyrgios admitted before departing the US Open this week that he had "no idea" how to make good on his extraordinary promise after now going five years since reaching a grand slam quarter-final.
But Laver, in New York to mark the 50th anniversary of his second calendar-year grand slam sweep, believes the answer is "obvious" - knuckle down and ditch the on-court theatrics.
"I don't know if he's deliberately aiming for publicity or whether he's aiming at individual things that he wants to accomplish, but that's the one thing he lacks, is discipline," Laver told AAP after being feted at a luncheon to commemorate the Australian winning of all four majors in 1969.
"And if he got some discipline, then most things come pretty simple.
"You don't interfere with your talent and that's what he's doing, is interfering with his own ability."
Arguably tennis's greatest ever player, Laver said "you'd have to be superhuman" to take on the role of coaching Kyrgios.
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But the 11-times major champion does see plenty of upside to Kyrgios's game - if only the mercurial star could earn to control his emotions.
"He's got probably the best serve in the game and so he knows how to win, but he has to apply himself and that's the one thing that's been a problem for him," Laver said.
"Tennis is a mental game in many ways and he's letting too many things get into the game of tennis."
No suspension: Laver
Laver pointed to how Kyrgios lost the plot in Cincinnati last month after receiving a code violation for exceeding the shot-clock time limit between points.
Once something sets him off, he struggles to regain focus, Laver said.
"That is his downfall," he said.
"Then that clicks into something else.
"I've seen him play great matches. His last loss here, he behaved perfectly fine, but I listened to someone - I think it was McEnroe, who was saying 'you better watch out now because he's had a mis-hit, or he thinks he was challenging a call and that could stir him up.
"That's what John was saying. That's what does it.
"A lot of times that's bad news for someone like Nick, because he may replay the mess in that match somewhere and it will say what McEnroe has said and now he's angry at that and so he'll remember that until he goes on to court to another match."
Laver, though, doesn't believe Kyrgios needs a suspension to get his act together and expects the 24-year-old to again thrive at this month's Laver Cup in Geneva.
"He likes team competition and I think that that brings out the best in him," Laver said.
"A lot of times you could say: 'Well, how could you pick him when he gets angry?'
"But we know him as a different person. He gets into a team competition and you could see when he's sitting on the sideline as they do, Europe and the Rest of the World are there, and he's the one cheering all the team.
"So he's a huge asset to the person on the court and so it works both ways."