Mercedes motorsport chief Toto Wolff on Monday played down expectations for the Formula One season after the team's top test times in pre-season testing in Barcelona.
"I have to dampen them because they are quite simply not realistic," he told dpa.
"It is of course pleasant to be at the front in testing but it means nothing."
Nico Rosberg posted the fastest time in winter testing on Sunday on the Circuit de Catalunya, a day after teammate Lewis Hamilton had also set the pace in the Mercedes W04.
It has led to hopes that after a disappointing season, Mercedes could be a real challenger when the F1 title begins on March 17 with the Australian Grand Prix in Melbourne.
However Wolff, who has replaced Norbert Haug as motorsport chief, said it would be wrong to draw any conclusion from the tests.
"It is perhaps a cliche but test drives and races are two different things, and we are there to race," he said.
"I don't think you can interpret too much into the test results. It was incredibly cold here and the teams drove with different fuel loads.
"You could theoretically deduce if a car is right or not. The truth is though you can't see anything. (World champions) Red Bull for example showed nothing. We won't know until Melbourne what's really going on."
Mercedes followed its test program without worrying about what other teams were doing, Wolff said.
"We worked out our plan and drove what we wanted, but not to impress anyone or to bluff," he said.