Nadal had to battle hard to get through his round of 16 clash against Nikoloz Basilashvili on Sunday evening.
And the world No 1 will now take on Dominic Thiem in the quarter-final tomorrow.
Meanwhile, Federer is yet to drop a set at this year’s US Open and Djokovic is enjoying a rich vein of form this summer.
And Moya believes one of the tennis legends will challenge Nadal for the final Grand Slam of the season this week.
“Djokovic is close to his best level and Federer is still a candidate for the most important titles,” he said, when pressed for his tournament favourites.
“But both are on the other side of the draw.”
Nadal’s clash with Basilashvili is likely to have taken a lot out of him.
And Moya admits he has to remind the clay-court expert that he is not a youngster anymore.
“I am trying to convince him in some things, not only me, but also the whole team,” he said.
“He still believes to be 20 years old, he wants to play in every tournament and in any place, win at every tournament and be at 100 per cent of his abilities every day, and that’s not possible at this stage of his career.
“We try to help him in any possible way, making him more aggressive and bringing some little changes to his game.”
Nadal meets Thiem in the last eight this week, while Djokovic and Federer will take on Joao Sousa and John Millman respectively in the round of 16.