The former British world number four, who represented his birth country Canada until 1995, believes the Swiss ace has a "clever" plan to ensure his long-term rival does not overtake him in terms of winning major titles which will ensure his status as one of the all-time greatest, and the greatest of this era.
Nadal and Federer are separated by 1960 points at the top of the ATP rankings and with the former not playing the upcoming Swiss Indoors in Basel, the latter has a chance to close the gap by a further 500 points if he wins the event.
But Federer said recently that the world number one ranking is not his main priority and indicated that he could skip either Basel or the Paris Masters as winning the ATP Finals in London is his main priority going into the final stretch of the campaign.
Rusedski labelled the ATP Finals as the fifth major tournament of the season, and believes Federer wants to win it so that he can boast winning more major honours than Nadal in 2017 and thus maintain his control as the best player overall. They currently have six apiece including the four Grand Slams between them - Federer won the Australian Open and Wimbledon to make it 19 majors, while Nadal picked up the French and US Open titles to make it 16.
"Roger is very clever," Rusedski said, as quoted by Sky Sports. "Even if he doesn't play [at Basel and Paris] and get to world No 1 but he wins more Masters series, they have two Slams apiece and then wins in London he will have actually won more of the bigger titles."
"Because that [the World Tour Finals] is probably the fifth major if you are looking outside the majors," he explained.
"Roger is thinking of the bigger picture all the time. Really the only player to threaten him as the greatest player of all time is Rafa. He [Nadal] has equalled [beaten] Sampras with 16 majors – Roger has 19.
"There is a five-year difference between the pair. Rafa, apart from the little strapping on his knees in the final, has looked very healthy. He [Federer] is going to try and keep Rafa away from having more majors than him," Rusedski added.