The Frenchman joined Nissan in an all-new line-up, partnering compatriot Sacha Fenestraz at the Japanese manufacturer ahead of the first season of the Gen3 regulations.
Nissan's pace looked generally impressive in testing at Valencia across the works team and at McLaren, and Nato topped the one-hour session tacked onto the end of the Thursday media day.
However, he explained that it had taken "a lot of energy" for him to adapt to the team, particularly with a number of changes behind closed doors following its takeover of the e.dams race team, and that the team is perhaps "not as ready" as others on the grid.
"Changing environment, it's been a really short time between the end of the season and switching to this car, learning the car; the steering, new software, new people, and to develop the car at the same time," Nato told Motorsport.com.
"It's like you have time for nothing else basically. So this is something for sure takes quite a lot of energy. I have to deal with it, same for the team, it's not easy for them because it's been quite a few changes for the team as well in terms of organisation.
"There's a lot of things for sure where we are not fully ready yet, and it will take a bit more time. For sure we see an advantage for teams like Jaguar which are working together with the same drivers.
"In the position we are, we know where we have to improve. If we are in the game to win in Mexico, good!
"If not, it's not the end of the world because we know where we have to improve and we know we are not as ready as some people maybe at the moment."
Nato explained the differences in adapting to the new car, and the tight timeframes involved in getting used to its handling and in maximising energy recuperation, which operates in a different manner to the Gen2 car.
He also joked that the heavier steering in the new car had led to more drivers spending their off-season publishing social media posts of their trips to the gym.
"Yeah, it's very different to be honest, compared to the Gen2 car - new tyres, completely different car in terms of downforce," Nato added.
"Steering is very heavy, so that's why you see all the drivers pushing in the gym on Instagram! But every car you drive is different, like just running the Venturi and the Jaguar - they were Gen2 cars, yeah, but the setup was already different.
"So you can imagine this car being like completely new as well. Way to regen is also affecting your driving style compared to Gen2, so that's why it's a lot of new things to learn in a really short amount of time - and it's our job to fight against the timing."
