Valtteri Bottas insists there is nothing "fundamentally wrong" with Mercedes' 2019 car.
The Finn was asked about the apparent half a second gap that separates the reigning champions from Ferrari after the first winter test.
"Ferrari seems to be ahead of us at the moment," Bottas admitted. "That's a fact."
He cautioned that the situation could be different by Melbourne, particularly if rumours are true that Mercedes is looking into following Ferrari's lead with the front wing design.
Explaining Mercedes' problem, Bottas said: "The tyre window is very small and the balance is on a knife's edge. We have problems in some corners and bigger problems in some others.
"But it also does not feel like something is fundamentally wrong with the car."
Speaking to Sky Italia, Bottas' teammate and reigning world champion Lewis Hamilton would not talk specifically about Mercedes' apparent deficit to Ferrari.
But he admitted that Mercedes could be set for "our most difficult year".
"I also know that I have the best team that knows how to find the way to the top.
"Tests are tests," Hamilton insisted. "At this moment it is completely irrelevant how fast we are. What matters is how fast we are in Q3 in Australia."
Team boss Toto Wolff denied that Mercedes is "sandbagging".
"You have to find a balance between not showing all your cards and developing a car that is representative of what you take to Melbourne," he said.
"We can see that Ferrari has done a good job, but other years have looked like that as well," Wolff added.
