Mercedes tech boss James Allison sees Red Bull as the German outfit's main challenger this year, based on what he's observed so far in pre-season testing.
Daniel Ricciardo put a new unofficial lap record of the Circuit de Catalunya on the board on Wednesday, clocking in at the end of the day with a mammoth 165 laps under his belt.
The Aussie's trouble-free session and impressive performance prompted Allison to now view the Milton Keynes-based outfit as a clear and present danger for Mercedes.
"I think there's three quick teams and there's no doubt that Red Bull are going to be people that we're going to be fighting with this year," Allison told Sky Sports.
"There's clearly no doubt about that.
"It's still not possible to say for sure if we've got our nose in front of them or they've got their nose in front of us, but you can say it's close."
After last week's botched sessions, teams are really getting down to business in Barcelona, freed from the vagaries of the weather, and are ramping up performance.
Allison admits he's impressed by the speed of Red Bull's RB14 in its current guise, and he also knows there is more to come.
"I don't know what their engine plans are, but looking at what they've brought here, I'd say they've still got some bodywork to bolt on before Melbourne," says the Mercedes engineer.
"But no one really sandbags. There's no point in sandbagging. You're here to test. And you're only going to do a valid test if you find out what your car can do.
"The thing you can do to change the absolute pace is to have more or less fuel in the car, to have the engine turned up more or less depending on what particular test you're making with it."