With strong backing from Banco do Brasil, the Brazilian raced for Sauber in 2015 and 2016 but lost that sponsorship and seat for this season.
But Nasr, 24, says he never lost hope.
“I achieved my training goals, gaining almost three kilos of muscle, and if I had to drive one of these cars tomorrow, I would be ready,” he told Brazil’s Globo.
“Of course I still have the will and the hope,” he explained. “I think that for 2018 there are open doors that can be worked on.”
However, he acknowledged that there are also still major obstacles to overcome.
“Everything depends on the current situation in our country, which is delicate, but I do not want to discourage any of the people who support me,” said Nasr.
“The chances of driving an F1 car this year do exist, but they are small. Because if you look at most of the big and medium teams, they already have third drivers under contract.
“It should have been arranged last year, but with all the turmoil, the timing for a reserve driver seat was not favourable,” he said, referring to speculation Banco do Brasil negotiated to potentially buy into Force India, and the change of ownership at Sauber.
Nasr said: “Now, none of this will keep me from getting a place in 2018.”