Golf's most prolific major winner, Jack Nicklaus, says Rory McIlroy must improve if he is to dominate the sport.
McIlroy goes into 2017 with only Jason Day above him in the world rankings and with four major titles to his name.
Nicklaus believes the 27-year-old from Northern Ireland now has to decide whether he wants to try to become the sport's greatest player.
Speaking to BBC Sport, the 18-time major champion was also optimistic about golf's future but renewed his call for a cut in the distance the ball travels.
In recent years Nicklaus has developed a strong friendship with McIlroy, who often practises at the 76-year-old American's Bears Club in Jupiter, Florida.
"Rory is one of those young men who has got a tremendous amount of talent," Nicklaus said.
"He has won and played on his talent to this point. If he wishes to dominate and go forward then he's got to improve."
Nicklaus warned that standing still at the top of the game means only one thing - quickly being passed. And he believes the UK's leading player is now approaching the prime of his career.
"He has to work hard, he's got to focus on what he is trying to do and it is up to him. Certainly he has all the tools to be able to do it - it is just whether he has the desire and the willingness to give up some other things.
"And that's his call. I mean, whatever Rory does, he has established himself as one of the great players that has ever played the game.
"Whether he wants to be the greatest player to have played the game, that's his determination and it's his decision whether he wants to make that effort to try to do that."
The 2017 season is likely to be a pivotal year in McIlroy's life with his wedding to fiancee Erica Stoll rumoured to be scheduled for the weeks following April's Masters.
Nicklaus famously combined a successful family life, bringing up five children, with collecting a record number of majors and an astonishing 118 tournament victories worldwide.
"It's just management of time," Nicklaus said. "When you are young and single and just one dimensional you pretty much can do things at your leisure.
"Once you start getting married, having a family, other business interests, then you've got to learn how to manage your time and use it efficiently. He'll learn that."
McIlroy has won two US PGA Championships as well as the 2011 US Open and 2014 Open. Next April he will arrive at Augusta seeking, for the third time, to complete a career grand slam.
"I think he will win the Masters [some day]," said the man who donned the famous Green Jacket on a record six occasions.
"He certainly has the type of game that would do well at Augusta and he has done well before - he just hasn't finished it."
And Nicklaus says McIlroy should not be put off by the hype that will accompany his continued attempts to land the one major to have eluded him.
"The media are going to focus on this because he hasn't won it," Nicklaus added. "He'll win it. He's a good player."
Although Nicklaus says he feels McIlroy needs to improve, the American veteran refuses to be drawn on specifics.
"I always felt like I was climbing a mountain and trying to get to the top of it," he said.
"And once I got to the top I was probably close to my mid-forties. And then I thought, maybe it's time to take a slide down the other side. But as you're playing and working at it you have to keep climbing and trying to get better."
'Golf needs to change'
One could apply this analysis to his views on the game in general. For decades he has been heavily involved in the business side with his course design company. Nicklaus also hosts his memorial event on the PGA Tour.
"I think tournament golf is very healthy," Nicklaus said. "Anything stagnates at one point or another and has to figure out how to reboot and move forward.
"And I think they've done a pretty good job of it. I think we are now moving back in the right direction."
But he hates the fact that golfers can routinely propel the golf ball more than 300 yards off the tee. "It is the most ridiculous thing in the game," he said.
"I mean, who cares how far it goes as long as it is relative to the other person. If a golf ball goes 20% shorter it is not much different to what it was 20 years ago.
"Some of the biggest problems we have are the cost of the game, the amount of time it takes to play, the difficulty of the game. All those things are things that can be addressed with one fell swoop with the golf ball.
"We can play the game faster, play the game cheaper, play the game a little less difficult. It takes less land, it takes less water, takes less chemicals - all kinds of things that help us."
And he has no time for the leading golf officials who celebrate the fact that the likes of McIlroy can generate gasps of awe from watching galleries through their prodigious hitting.
"When I belted it 280 yards they thought that was pretty good too," Nicklaus said. "Before me, when [Ben] Hogan hit it 250 yards, they thought that was pretty good.
"I think the fans get used to what they are looking at. I don't see a change in the golf ball soon but I think common sense says you should do it."
It's also clear that Nicklaus believes fans will see more McIlroy majors in the coming years, especially if the Northern Irishman is able to make the most of his vast potential.