Nico Rosberg says data that his Mercedes team has gathered from pre-season testing suggests Ferrari is close, and could even be ahead at the start of the Formula 1 season.
Although Mercedes has enjoyed a brilliant two weeks of running – completing almost 20 race distances – it opted against chasing headline times while Ferrari appeared to be more performance orientated.
Mercedes' baseline pace left some rivals convinced that the German car manufacturer could be even further ahead this year than last, but Rosberg says that is not what his team believes.
Speaking about the threat of Ferrari, he said: "They have been very quick for sure.
"All the teams have their strategists so we know more or less what fuel the other teams are running and they know our fuel.
"So we know more or less where we are compared to Ferrari – which is why I say for sure it is close. But we are not sure if we are ahead or behind."
When asked by Motorsport.com what he would say to those who suggest Mercedes is in a league of its own, he said: "I just say let's wait two weeks...I hope they are right."
Rosberg welcomed the solid start that Mercedes had made to the year, but remained cautious about the overall potential of the W07 package.
"It has gone really well for sure," he said. "Of course, the most important thing is the speed – which we are not 100% sure of.
"We know Ferrari is very close, so it can go either way. But apart from that, everything else has gone really, really well. Definitely I am ready for Melbourne."