Dr Helmut Marko has said that he thinks Mercedes continue to lead the pack in 2017.
Hopes were high that Red Bull or Ferrari would catch up to the reigning world champions thanks to the new regulations, but Marko thinks Mercedes is still ahead.
"The driveability of their engine and the packaging are incredible," the Red Bull official told Auto Motor und Sport.
Ferrari have looked closest to Mercedes so far, but it is also widely believed that Red Bull are yet to show their full hand.
"We are still driving conservatively," Marko admitted. "Let's see how it looks when we have full power.
"You can hear that Mercedes is doing the same thing."
As for Ferrari's apparent big leap over the winter, Marko commented: "It depends on how much fuel they are using. "As late as [Sebastian] Vettel was braking into the first corner yesterday, there can't have been much in there."
It is also believed that Red Bull will add a range of aerodynamic appendages at the second and final Barcelona test, but Marko said: "Our car is beautiful. And normally beautiful cars are fast.
"Why should we change something?"
The 2017 calendar begins with the Australian Grand Prix on March 26.
