Federer holds the record both for the most time spent at No 1 (302 weeks) and the longest consecutive run at No 1 (237 weeks).
However, he currently sits second in the world rankings, more than 1,000 points behind his great rival Nadal.
But as the 36-year-old begins to wind his career down – Federer skipped the entire clay-court season in 2017 and played a total of just 12 tournaments – Wilander reckons he will become less interested in the rankings.
“I’m not sure if he [will become] the oldest No 1,” Wilander said.
“I’m sure that he is now not really worrying about [the ranking] because he’s winning Grand Slams.
“Maybe towards the middle of this year he might worry about being No 1 in the world but he has so many ranking points to defend in the next few months with Australia and also Miami and Indian Wells.”
Federer will almost certainly once again skip the French Open and the rest of the clay-court season to preserve his energy.
The Swiss took six months off last year to deal with knee and back injuries but returned in 2017 to win two Grand Slam titles including a record eighth Wimbledon crown.
And Wilander, who won seven Grand Slams including three in 1988 to end the year as No 1, thinks Federer’s game has changed to allow him to him to challenge at the biggest tournaments.
“I think that you have to allow the natural evolution of not only your game but also your personality,” Wilander added.
“Suddenly, you’re a husband and father and things change in life that means things most probably have to change on the tennis court.
“The most obvious change is always to become more aggressive and play shorter points just like Roger Federer is doing, just like Rafael Nadal is doing.
“They’re both completely different players from what they used to be. That’s the natural evolution.
“The tendency is to try and get back to what you used to do.
“But the fact is that every year the game moves in a direction of being faster and players are harder.
“In general, they get stronger and serve bigger – and you’re going to have to follow that.”