Rafael Nadal, Roger Federer and Novak Djokovic dominated tennis for the best part of two decades, but it is debatable whether Carlos Alcaraz and Jannik Sinner can emulate that, Nadal's former coach Carlos Moya told AFP.
World No 1 Sinner, 23, and the 22-year-old Alcaraz have garnered seven Grand Slam titles already between them.
By comparison, Nadal, Federer – both of whom have retired – and Djokovic, a trio known as the 'Big Three', swept up 66 from 2003 to 2023.
Alcaraz and Sinner are gearing up for the French Open with the former the defending champion.
"To achieve what these guys have been doing these last 15, 20 years, that's something that I don't know if we are going to see in the future," Moya, a former world No 1 and 1998 French Open champion, told AFP from Mallorca.
"I can tell that in the next couple of years, this rivalry is going to be there.
"Then maybe five years, seven, but so many things can happen.
"Injuries and family problems. Mental health issues, you don't know what's going to happen in three, four, five years' time."
Moya, who will return to Roland Garros on Sunday as organisers pay tribute to record 14-time French Open singles champion Nadal, said rivalry was key to the longevity of the sport's three most successful men's players of all time.
"They pushed each other to the limit," said the 48-year-old Spaniard.
"Without the other guys, Rafa, maybe he would have retired four or five years ago with 16, 18 Grand Slams."
Moya achieved a lot in his career but he said he was in awe of that trio.
"My ambition was never to be one of the best players ever because I didn't have the level to dream about that," he said.
"I mean, my dream was to win a Slam, to become No 1, but was never to win multiple Grand Slams or being No 1 for a few years.
"With these guys, it's a different game.
"I mean, their ambition is unbelievable and how mentally stressful is that what they're doing? It's something that people are not aware of."
'FAKE NEWS'
Moya and Nadal's relationship goes back decades but the older Spaniard said his role when he joined the team in 2016 was to strike a balance between being a coach and a friend.
"I knew him so well," said Moya.
"I knew him since he was 11 years old. I could know what was going through his mind, how he was feeling."
Moya said there were the highs of "eight Grand Slams" but also the "difficult moments" of "hard losses in Grand Slam finals" and injuries.
"When he's going through that, I mean, you have to be supporting him.
"You have to be his friend. You have to be the person he can talk to."
Nadal hanging up his racquet last November put Moya back on the market but he says he is not ready to return to the grind of the tour.
"To be on the tour, in my opinion, you have to be 100 per cent ready for that mentally," he said.
"I didn't feel I had the energy and also after being with Rafa, it's hard to be back on the tour again with another player."
As for a story linking him with Sinner, Moya said it was "fake news".
"As soon as there is something new in my life, I will announce that myself.
"I will not wait for a random Russian website to decide what I'm going to do," he added.
Moya has retained his ties with tennis as he is a team captain for the Legends Team Cup, pitting his wits against Australia's Mark Philippoussis and American James Blake.
Each has a five-man roster – Moya's includes 2020 US Open champion Dominic Thiem – which will face each other twice with prize money of $1 million at each event.
The top two teams progress to the final with a $5 million prize and the Bjorn Borg Trophy at stake.
For Moya, it is ideal as he says it is like going from being a football club coach to being in charge of a national team, removing the daily pressure.
It means he can devote his time to his wife and three children.
"My kids are 14, 12 and 11," he said.
"I'm enjoying the time I'm spending with them, before you know it they're going to be 18 and they probably fly away from home."