Nick Kyrgios must get fit or risk falling short of his potential, according to French Open winner and Australian tennis great Ken Rosewall.
On the 50th anniversary of his second Roland Garros triumph, the first of the Open era, and on the eve of this year's tournament, Rosewall issued a warning to the Australian No.1.
Get fit or fall behind.
"In some ways, he's his own worst enemy," Rosewall, 83, said.
Kyrgios is currently battling an elbow injury which could yet force him to withdraw from the clay-court grand slam starting on Sunday.
The 23-year-old will test his fitness by playing doubles with friend Jack Sock at this week's ATP event in Lyon.
He's missed six weeks on the tour and was last seen in action in Houston at the US Men's Clay Court Championships.
The world No.23 has an impressive 11-4 record this season - with two of those losses coming to Alexander Zverev.
But Rosewall, known for his commitment to physical fitness, says Kyrgios will only end Australia's wait for another grand slam champion with a deeper focus on training.
"With the leading players, there's been a few obstacles," Rosewall said at Melbourne Park on Tuesday.
"Nick is one that has more potential than anybody.
"He does have a physical problem, which is not his fault, (but) certainly he needs to work a little bit harder on his physical fitness.
"He doesn't seem to play any long matches.
"I'd like to see them working harder on their game ... it might bring better results."
Kyrgios has a 5-2 career record in matches that go to five sets, winning four of six best-of-three-set matches on tour this season that have gone to a decisive third set.
He has struggled with back, hip and knee issues over the past two years, which have restricted him from playing full seasons.
Should the Canberran take his place at Roland Garros, he won't be among the tournament favourites, given his best result is a third-round appearance in both 2015 and 2016.
Rosewall claimed the tournament twice - in 1953 as an amateur and 1968 as a professional.
He said emerging clay-courter Alex De Minaur stood the best chance of being the first Australian winner at Roland Garros since Rod Laver in 1969.
"He's the next one," Rosewall said.
"He's a good chance of winning majors, especially on clay. He's good on most surfaces."