Mercedes say Ferrari are closer to their pace than they looked during the first qualifying session of the new F1 season in Australia on Saturday.
Lewis Hamilton headed team-mate Nico Rosberg to a one-two, with Ferrari's Sebastian Vettel 0.652 seconds adrift.
Mercedes F1 boss Toto Wolff said: "We see the pace and the threat in that car; they just haven't been able to translate it into lap time yet."
Rosberg said the gap was "not real" and Ferrari would be quicker on race day.
The first race of the new season gets under way on Sunday at 05:00 GMT, with coverage on radio 5 live from 04:00 GMT and online from 03:30.
Both German Rosberg and British world champion Hamilton pointed out that Vettel had only done one run in final qualifying, while Mercedes had done two.
"If Sebastian had gone out again he would have been quicker, probably by another 0.2secs," Hamilton said. "It's closer this year but it is still a decent gap."
Hamilton said he expected there would be races this year when the gap would narrow but added that predicting form for the season was "a big guess".
Vettel said he believed he could compete with Mercedes for victory on Sunday.
"In the race you can always try to create something," said the German. "I hope we can definitely put more pressure than today on both of them in the race."