Federer has not been at the top of the rankings since 2012.
However, the Swiss legend can return there this week if he reaches the semi-final of the Rotterdam Open.
The 36-year-old would become the oldest men’s No 1, overtaking Andre Agassi who held it at 33.
He would also break the record for the longest gap between stints at the top, which is once again currently held by Agassi at three years and 142 days.
But Nguyen believes Federer’s reduced schedule, where he missed the entire clay court season last year, shows he is not that bothered about returning to the top.
She says that is opposite to current No 1 Rafael Nadal, who she claims puts his body under increased scrutiny to get the points required to be No 1.
“This is a conversation we’ve had about Rafa for the last 10 years,” Nguyen said on the No Challenges Remaining podcast.
“The way that he plays the sport is not sustainable, that’s why there has always been questions about whether or not his body could endure the way that he plays.
“That is what’s frustratingly amazing about Roger. The way that he plays, he can do those things.
“That is his benefit and he is allowed to take advantage of it.
“If Rafa can’t take advantage of it because he has to play a full clay court season because he wants all the points because he cares about being No 1, like Roger doesn’t care about being No 1.
“If he cared about No 1 he would have adjusted his schedule accordingly.”
Roger Federer’s chances of returning to No 1 have been boosted by recent injuries to Nadal, who pulled out of the Australian Open at the quarter-final stage due to a thigh strain.