Nadal’s first win at the Paris Masters two weeks ago ensured he would end the year as world No 1, the oldest man ever to do so at the age of 31.
However, he later pulled ouf of the tournament and played through obvious pain during ATP World Tour Finals defeat to David Goffin on Monday.
The Spaniard subsequently ended his season because of a knee injury, a problem that he has encountered repeatedly during his career.
But Federer refused to blame scheduling or court conditions for Nadal’s injury, which has come with Andy Murray, Novak Djokovic, Stan Wawrinka, Kei Nishikori and Milos Raonic already sidelined by injury.
“Shave 10 years of our age, and we probably will do better,” Federer said with a smile after booking his place in a record 14th ATP World Tour Finals semi-final with a win over Alexander Zverev.
“A lot of the guys are just touching 30 plus.
“Back in the day, at 30, a lot of guys were retiring.
“Edberg, Sampras, it was like normal at 29, 32, to start looking towards the end of your career.
“Now you guys expect everybody to play till 36.
“When somebody is injured at 31, it’s like, ‘Oh, my God, how is this possible?’
“Actually, it’s a normal thing.
“If either you retire or you take a sufficient break so when you do come back you maybe have another few years left again because you really made sure your rehab is good.
“So I think for the most part it’s age, coincidence.”
He added: “The season has been the same for many, many years, as we know.
“I think just when you get older, you maybe have to manage your schedule maybe a little bit differently.
“But some guys, they just go maybe all out for 15 years, and they do it until you sort of break down, then you just reset.”