The ageing duo ruled the sport last year, winning all four Grand Slams between them despite a new generation of young stars - led by Alexander Zverev - breaking on to the scene.

Rusedski is a huge fan of Zverev but he thinks the whizzkids will be made to wait by Federer and Nadal.

"The change of the guard will happen in two years' time, " Rusedski said speaking at the Champions Tennis event at the Royal Albert Hall.

"I'm expecting Federer and Nadal to still be at the top of men's tennis in 2018 and hopefully Andy Murray gets healthy again. That's the big question mark: when is he going to be back? I hope he doesn't rush it.

"Novak Djokovic is more psychological than his elbow and I think it's an easier transition to get back. He will be in the mix with Roger and Rafa."

Nadal ended the season withdrawing from the ATP Finals with a serious knee injury but he still finished world No 1.

Rusedski thinks the Spaniard, 31, will find it hard to hold on to top spot and instead thinks Federer will reign supreme in the rankings.

Rusedski said: "I think Roger could be number one again because he's had that six months off and he's had an incredible year.

"To enter 12 events in the year and win seven of them is incredible.

"Rafa has to enter so many events and play back-to-back to stay No 1. I don't see the gap changing just yet with the new generation but it's starting to get closer.

"In 2019, that's when they'll take over. What Roger has done is incredible, what Rafa's done is incredible.

"We've got Zverev and once Nicky Kyrgios gets his mind together and has a good coach,...

"Then you've got Denis Shapovalov, a Canadian, who is exciting but he's two or three years away from the top of men's tennis.

"There's lots of names to look forward to but I think we're just blessed to have Roger and Rafa playing so well.

"Who'd have picked, after 2016, for Roger and Rafa to be battling for World No 1?"