German world number three Zverev, who is seeded to meet Djokovic in the semi-finals, said Nadal seems to have shrugged off the recurrence of a foot injury which saw him limp to an early defeat in Rome last week.
“I just watched Rafa practise and it’s funny because all of a sudden his forehand is just 20 miles an hour faster. He moves lighter on his feet,” said Zverev.
“There is something about this court that makes him play 30% better, just being on this court.”
World number one Djokovic, bidding for a third Paris title to move level with Nadal on 21 Grand Slams, comes into the tournament with a sixth Italian Open under his belt.
The Serb, who turns 35 on Sunday when the French Open starts, is also fired up by missing out on his Australian Open defence in January when he was deported from Melbourne over his refusal to be vaccinated.
“I think Novak right now, as well, he’s finding his form again,” added Zverev.
“He’s been playing better and better each week that he’s been playing on the clay courts. He’s been playing fantastic in Rome.
“Those two guys (Djokovic and Nadal) are still the No. 1 and 2 favourites for me.”
Zverev, a semi-finalist at Roland Garros in 2021, is seeded to face new teen sensation Carlos Alcaraz in the quarter-finals of a top-heavy draw where Djokovic and Nadal could also clash in the last eight.
Alcaraz, 19, and bidding to become just the eighth teenager to win a Grand Slam men’s title, has a tour-leading four titles this year.
Three of those have come on clay in Rio, Madrid and Barcelona.
In Madrid, he defeated Nadal, Djokovic and Zverev on his way to the title.
However, Zverev warned that Alcaraz lacks the experience of Djokovic and Nadal when it comes to gruelling five-setters on clay.
“It takes a lot more than just playing good tennis to win a Grand Slam,” said the 25-year-old German who managed just four games in his final loss to Alcaraz in Madrid.
“The dream of winning a Grand Slam. That’s what the biggest difference is. We start playing tennis because we want to win the biggest titles in the world.”
Zverev has yet to win a Grand Slam title, the closest he came was at the 2020 US Open final where he surrendered a two-set lead to lose to Dominic Thiem.
He comes into Roland Garros having made the semi-finals on clay in Monte Carlo and Rome as well as finishing runner-up to Alcaraz in the Spanish capital.
“I’m not saying I have lost matches because of my physical ability,” he added.
“No, I think I have lost matches because I have put a lot of pressure on myself winning a Grand Slam. That is more the reason why I maybe haven’t won one yet.”