The duo returned from long lay-offs to experience career resurgences in 2017 as they both split the four Grand Slams between themselves and won a combined 13 titles to truly turn back the clock.
The feat is all the more impressive considering many had completely written them off during the dominant spells of Novak Djokovic and Andy Murray in the last few years, as they now occupy the top two of the ATP tennis rankings with Nadal currently leading the pack.
With Federer's win over Marin Cilic in the Australian Open final last month, the career renaissance looks set to continue as Monfils heaped praise on the 20-time Grand Slam winner.
"Definitely Roger must be called the gentleman of tennis," Monfils said, as per Express. "We're not talking about just one champion, it's already a legend.
"Michael Jordan is in basketball and we have him in tennis. I am impressed by his personality. I know him personally, he's my friend. His legacy on the court will last a long time and his that is admirable."
The Frenchman also reserved praise for 16-time Grand Slam winner and longtime friend Nadal as he called him an "incredible man" before labelling the two of them as legends.
"I met Rafa when I was about 11 years old. We played from when we were small," Monfils added, who boasts a combined 6-22 win/loss record against the pair. "There's Roger, but we have an incredible man in Rafa.
"The shape of his shots, his slice... I have a lot of respect for him. I think Roger and Rafa are already legends."
Monfils is currently taking part in the Ecuador Open and will face Casper Ruud in the round of 16 on Thursday (8 February).