All three players are competing at the Italian Open this week as part of their final preparations for Roland Garros.
However, there have been an increasing number of upsets caused by the younger players over the last couple of months.
Nadal is aware of the uprising of the NextGen stars and believes himself, Federer and Djokovic losing more frequently is normal.
“Roger is 37 years old, I am almost 33, Novak is 32,” Nadal said.
“Winning everything we have won in the last 14 or 15 years is something that does not happen much in the history of tennis, which means it’s complicated.”
Nadal will open his Italian Open campaign against the winner of Richard Gasquet vs Jeremy Chardy.
The world No 2 has been in poor form having not won a clay title this season.
But he does not feel like he has been playing badly.
“I have a lot of work to do, I have Chardy or Gasquet at my premiere, this is my picture, everything else does not matter to me now,” Nadal added.
“I feel good, it’s true that I have not won titles on clay.
“But for example in 2015 I won in Buenos Aires and right now I feel much better than that year, sometimes winning a title does not make much difference.
“It’s true that I lost a couple of tournaments, but it’s also true that I was close to winning.
“I did not play well enough to win, but I did not play that bad either.”
Nadal’s recent form has seen him lost to Stefanos Tsitsipas in the Madrid Open semi-final last week.
Before that, he suffered surprise losses to Fabio Fognini and Dominic Thiem in Monte Carlo and Barcelona.