The 36-year-old veteran enjoyed a renaissance this past year as he took his overall Grand Slam tally to 19 with wins in Australia and at Wimbledon, while his overall record was impressive with just five defeats in 57 matches.
However, Federer opted to take breaks from the tour, completely skipping the clay-court season and subsequent French Open in the process, in order to prevent his fitness suffering for tournaments on his favoured hardcourt and grass surfaces.
It paid off for the Swiss, but Nadal, who also won two Grand Slams in 2017 and finished the calendar year as world number one, felt it was a gamble.
"He had a fantastic year," said the Spaniard.
"What he did is very difficult. Playing so less, being able to win almost every time you return to play is a very big risk.
"When it goes well, it seems it's right, but in truth it's very difficult that it happens the way it did.
"If you try it again, you may not be as successful as you were this year. But well, I am 31 and he's 36. I have my career and he has his own."