Red Bull is "far ahead" and it will be very difficult for rivals including Mercedes to catch up.
That is the claim of Nico Rosberg, who after a promising winter campaign for Mercedes struggled for pace in the new silver W02 in Australia.
"We have to say that Sebastian (Vettel) and Red Bull are far ahead of everyone," he told Sport Bild.
"In the chasing field, we want to play a serious role and improve on our fourth place of last year," added Rosberg.
The German marque's motor sport director Norbert Haug also admitted that catching up with Red Bull "will be difficult".
It was strange that it worked for McLaren but not for us
Also doubting Mercedes' ability to catch up by deploying aggressive car development is Helmut Marko, Red Bull's motor racing consultant.
"Very few teams can take a car and make it much more competitive -- besides us, only Ferrari and McLaren (can)," the Austrian told Sportwoche.
The first task for Mercedes will be to sort out the obvious problems seen in Melbourne, such as the malfunctioning KERS system.
"It was strange that it worked for McLaren but not for us," said Haug.