Felipe Nasr has played down Sauber's sudden leap from the doldrums of 2014 to the top of the Jerez timesheets.
The new C34, bearing the blue and yellow of Brazilian rookie Nasr's Banco do Brasil backing, has been at or near the ultimate pace ever since the first test of the 2015 pre-season began at Jerez.
But Nasr, while earlier admitting that engine supplier Ferrari has obviously improved its turbo V6, played down Sauber's leap from zero points in 2014 to head-turner in 2015.
"The fastest time means nothing in testing," he is quoted by Globo.
"I know what to expect from a team that went through what Sauber went through last year. We will not be on the front row of the grid."
Nasr, 22, admitted that when he set the fastest laptime of the day on Tuesday, he was equipped with Pirelli's soft tyres.
"It is important for me to have experience with everything I will have on the Grand Prix weekends," he said.
Nasr said he is happy with Sauber's progress so far, but is expecting Mercedes to once again set the pace when it really matters.
"I think maybe Mercedes is hiding a little bit of what they could do," he is quoted by Totalrace.