Toto Wolff has said that it is too soon to say Mercedes are still ahead of the field in 2017.
After the first of just two pre-season tests, the conventional wisdom is that Mercedes lead, Ferrari are close behind, and Red Bull are the third force.
However, Mercedes team boss Wolff told Osterreich: "Since we have these new rules, the teams are just trying to get a lot of mileage to know their cars.
"At Red Bull, we probably haven't seen the car that will be in Melbourne. But Ferrari is really fast."
McLaren chief Eric Boullier admits that a pecking order is not possible to assess after four days of running, but he said Ferrari's pace has been "surprising".
"We did not expect to see them on the pace with the Mercedes. Red Bull seems a little behind, but we do not have all of the information to judge," he is quoted as saying by France's Auto Hebdo.
"We may know a little more next week, but we really have to wait until Australia."
Boullier may be surprised with what he saw in Barcelona, but Red Bull's Max Verstappen seemed calm.
"Actually, nothing surprised me here," he is quoted as saying by Het Laatste Nieuws. "And I think everything is still within reach for us."
The 2017 calendar commences with the Australian Grand Prix on March 26.
