Rusedski can see Federer struggling to resume his career once his eventually returns from his 2020 break, largely enforced by the COVID-19 pandemic.
Speaking exclusively to RadioTimes.com, Rusedski said: "There's no reason Nadal and Djokovic don't go on for another two to four years, but Federer is the question mark.
"One more year left. Wimbledon, can he win Wimbledon? The Olympics? He's a year by year case, especially after having the knee surgeries as well. You're not getting the guy in 2017, I'm sorry. Time has passed on.
"Can he play well? Of course he can, but there are no surprises. The racket's been put in play, the style's been put in play, what is he going to bring to the table that is going to be new? You tell me. I can't imagine anything he can change to his game so people already know what's coming at them.
By entering your details, you are agreeing to our terms and conditions and privacy policy. You can unsubscribe at any time.
"When he won tournaments in 2017, the courts were particularly quick, the balls were quick, and he brought a style that people weren't expecting. They're expecting that style now, so they know what they're getting.
"Unfortunately, not like a fine bottle of wine like Margaux when it get to 40 years it goes up in value it, it gets every bit harder, the months you miss away from the game. Six months and 11 months in men's tennis is a huge difference.
"He can still play great tennis, but to win the Slams is another story. The Olympics is a huge priority for him to compete there because that's the one thing he doesn't have, a gold medal in the singles, that he's desperate for."
With a grin, he added: "You know, Andy Murray has two of them."
But who will end up the ultimate men's tennis player? Rusedski believes Djokovic will be the top dog once all is said and done.
"Both Nadal and Djokovic will both pass Roger Federer if they both stay healthy with the amount of Slams they've won.
"Djokovic will have it, but next year is going to define who will have it more or less because you give the French to Nadal, the opening part of the year is going to be interesting Down Under where Djokovic has dominated and Djokovic should be at 18, but he's at 17 after what happened at the US Open.
"It's between Nadal and Djokovic in my opinion. The opening salvo of the year Down Under will give us an idea of what's going to happen.
"If Nadal gets to 21 – I'd be shocked if he doesn't get the French again the way he played this year – then Djokovic needs to get multiple slams in a year from now because he's basically three behind. He needs to start getting two or three Slams a year now."
You can tune in to watch the ATP Finals on Amazon Prime Video starting this Sunday 13th November. Check out our full guide on how to watch the ATP Finals plus our comprehensive ATP Finals schedule.
If you’re looking for something else to watch check out our TV Guide.
