Having finished Friday's running almost a second slower than Mercedes, Sebastian Vettel is hoping Ferrari can improve ahead of qualifying.
The four-time World Champion was once again best of the rest behind the Mercedes as the Brazilian Grand Prix weekend got underway.
Third in both sessions on Friday, Vettel finished the afternoon practice 0.960s slower than Nico Rosberg.
And although the Ferrari driver feels bad timing in drizzle may have played a role in his deficit, he admits the Scuderia have some work to do.
"Overall it was a difficult day," he said.
"We didn't get the best timing for our run, so now we look forward to the analysis of our laps.
"Hopefully we can make a step forward for tomorrow and improve the car.
"Today everybody struggled quite a lot with the tyres: they seem even more tricky than last year, but then I think it was slippery for everyone.
"I tried to do the best I could, but maybe I wasn't quick enough. The car was moving around and sliding quite a lot.
"Hopefully tomorrow we will be in better shape."