A bright future for men's tennis can be glimpsed in the line-up for this year's ATP Finals, according to players young and old.

The seemingly immovable trio of Rafael Nadal, Novak Djokovic and Roger Federer remain atop the rankings with a combined age of 103.

But behind them the young guns are making big moves, and four of the eight players who will do battle in London are aged 23 or under, including the charismatic trio of Daniil Medvedev, Stefanos Tsitsipas and Alexander Zverev.

The German said: "There's a very strong group of guys. I think we'll see (young) guys all of a sudden start to win big tournaments, which we haven't seen for the past 10 or 15 years.

"I think the next two or three years are very exciting. The other guys are still here playing the best tennis in the world, they're still better than us, but I think the younger guys are improving quite quickly."

Nadal laughed at the suggestion his group rivals might make him feel old, saying: "I am 33-and-a-half, that's old to play tennis, I think young like a human person.

"I'm happy to be where I am today. Honestly I didn't expect to be where I am when I have been in the position of all of them. As Sascha (Zverev) said, it's an exciting moment.

"We can see here there's a lot of very young players, they're improving. It's the normal cycle of life. It's healthy for the sport, too. They are the future but they are the present. They have good competition between each other for the next years.

"They're going to fight for the same things. It's going to be good rivalries for our sport and I will be happy hopefully to keep competing with them for a while, but then I will be happy to watch them on TV."

Djokovic opens the tournament on Sunday afternoon against Italian Matteo Berrettini, another 23-year-old debutant, before Federer faces Dominic Thiem.

Monday afternoon sees Medvedev take on Tsitsipas, with Nadal having been given the maximum time to recover from an abdominal problem before he faces Zverev in the evening.