The recent success of younger players on the men's tour points to an "inevitable" shift at the top of the Men's Professional Tennis (ATP) rankings, said tennis world No.1 Novak Djokovic of Serbia.

The last four ATP Masters 1000 events – the most prestigious tournaments outside the Grand Slams – have been won by players outside the "Big Three" of Djokovic, Rafael Nadal of Spain, and Roger Federer of Switzerland.

Russian Daniil Medvedev, 25, won the ATP Finals and the Paris Masters titles last year and has already displaced Nadal to second place.

Hubert Hurkacz of Poland, Stefanos Tsitsipas of Greece, and Alexander Zverev of Germany have won the three Masters events this year with Tsitsipas the youngest of them at 22.

Djokovic: 'It's inevitable that it's going to happen'

While the 39-year-old Federer missed most of the last 14 months due to knee problems, Djokovic, who has won 18 Grand Slam titles, is more focused on chasing down the 20 major wins of Federer and the 34-year-old Nadal.

Djokovic set a new landmark of 311 weeks as tennis world No.1 on March 8, 2021, one week longer than Federer whose tally of a record 20 Grand Slam titles is now firmly in the Serb's sights.

The 33-year-old Serbian won his 18th major at the Australian Open in February.

He told reporters at the Rome Masters on Monday that the results showed there was a generational shift underway.

"There are guys like Tsitsipas, Zverev, (Matteo) Berrettini, (Andrey) Rublev that are winning against all of us and playing a lot and building their ranking points," the Serbian said.

"Medvedev as well, of course, and challenging for the top spots, Dominic Thiem has been there for many years," he added. "It's inevitable that it's going to happen. The change on the men's rankings, top of the rankings, is coming. Whether it's going to happen in a month or a year or whatever, I don't know."

"I'm not personally paying too much attention anymore to the rankings as much as I am to my game for the Grand Slams," he said. "Those are the biggest focus tournaments right now at this stage of my career."

Djokovic has made changes to his schedule to spend more time with his family and since his Melbourne win has only played the Monte Carlo Masters and an event at home in Belgrade.

"I think four tournaments before French Open is enough in terms of the match play," he said. "So I'm building my fitness and I'm building just my game slowly step by step in order to peak in Paris. That's definitely where I want to play my best."

Nadal: 'it's a tough year'

"For me, personally, it (the pandemic) has been tough," Rafael Nadal told The Telegraph in a recent interview. "It was difficult for me to keep going after the lockdown. The circumstances made me think about what was the right decision for my career: if I keep playing, or stop for a little more? It was not an easy decision."

"It has been a tough year, I really believe, for everyone," the 34-year-old said.

Speaking of young players, Nadal praised Tsitsipas ahead of their 2019 Australian Open clash.

"The young generation doesn't want to wait for big wins or titles; they are here now, with Frances reaching the quarters and Stefanos waiting in the semis. It will be a great year in terms of sharing the generations that make the sport special, and that would be interesting to watch," Nadal said.

Also, Nadal said Tsitsipas is a great player and "should remain at the top for a long time."

(With input from Reuters)