After his quarter-final win over Robin Haase in the Rotterdam Open last week, Federer overtook Nadal in the ATP tennis rankings to reach the summit for the first time since 2012.
Federer's return to the top was helped by Nadal's withdrawal from his Australian Open quarter-final clash with eventual finalist Marin Cilic last month due to a hip problem.
The Spaniard finished as a runner-up to Federer in last year's Australian Open and exiting in the last-eight saw him lose 840 points, giving the Swiss legend the opportunity to overtake him.
However, with Nadal expected to make a comeback at the Mexican Open in Acapulco that commences on Monday, 26 February, Federer's father Robert believes a return to the top for the 16-time Grand Slam champion is more than possible.
"How long he [Roger] can defend the top spot now is in the stars," Robert Federer told Swiss newspaper Blick, as per Express.
"Maybe only a few weeks – if Nadal plays well in Acapulco – it can be over very quickly."
Nadal, though, will not be able to regain the world number one ranking in Mexico next week even if he goes on to win his first title of the year.
The Manacor native, currently 345 points behind Federer, finished as a runner-up last year to Sam Querrey, which means he will only gain 200 points if he wins the event. However, he will be just 100 points behind if Federer opts to sit out of the Dubai Open, which takes place next week as well.
If that is the case, Nadal could return to the top of the rankings at next month's Indian Wells event as a win there would see him overtake Federer.