George Russell said Mercedes were “nowhere” in Friday practice at the British Grand Prix.
Russell and team-mate Lewis Hamilton were 12th and 15th fastest as they lagged more than a second behind Max Verstappen’s pace-setting Red Bull.
This was despite Mercedes introducing a new front wing, the latest in a series of recent car upgrades aimed at moving them closer to the front of the field.
Russell said the team “had to try to understand” their lack of pace.
Hamilton said: “It’s a tough car to drive and no matter what we do to set it up, it remains a tough car to drive.”
The seven-time champion said he felt no improvement when changing from the medium to the theoretically faster soft tyre.
“That shows that’s something’s wrong,” Hamilton said. “We’re missing something. And on the long run it didn’t seem too bad, so that’s a positive at least.
“George is over here with the set-up and I’m over here. He was saying I was thinking of coming over to where you are but your lap time is slow. And I was like I was thinking of coming to where you are.
“We will work on it tonight and hopefully we will come up with something for tomorrow.”
Hamilton’s race-simulation pace was more competitive. He was faster than the Ferrari of Carlos Sainz – which was second fastest on a single lap, just 0.022secs slower than Verstappen – but still considerably slower than the world champion’s Red Bull.
Russell said: “Definitely not our finest Friday. Conditions will be different tomorrow. We need to try to get to the bottom of it.
“The pace in first practice was looking quite good on the medium tyre. We thought we were right up there, if we took the soft.
“But in P2 we were nowhere and we just need to try and understand that.
“We see a small trend that when the temperature is hotter we seem to take a bit of a step backwards we have some ideas why that is.”
Temperatures at Silverstone on Friday, when 120,000 spectators attended the track, were in the high 20Cs but are expected to drop a little for the weekend, when rain also threatens.
Verstappen looked imperious, despite his small margin over Sainz, and his long run on a race fuel load was especially impressive.
The Dutchman’s race-simulation run was more than 0.5secs a lap on average quicker on the same soft tyre than team-mate Sergio Perez, with Sainz a little further behind.
Williams driver Alex Albon was an impressive third fastest, with team-mate Logan Sargeant fifth behind Perez.
Lando Norris was 14th fastest in the upgraded McLaren that impressed so much last weekend in Austria.
Ferrari’s Charles Leclerc did not get out in the session at all after the team discovered an electrical problem over the lunch break.
Fernando Alonso, third in the championship for Aston Martin, was only 10th fastest on single-lap pace, with team-mate Lance Stroll sixth, ahead of the Haas of Nico Hulkenberg, Pierre Gasly’s Alpine and McLaren’s Oscar Piastri.
Piastri, an Australian who is in his debut season, has on his car for the first time the upgrade that Norris debuted in Austria, while Norris has those parts in addition to a new front wing.
A number of the drivers said that they were struggling for grip, especially in the first session, as they tried a new, more robust Pirelli tyre construction for the first time.
Pirelli have introduced the tyre to lessen the risk of failures at high-speed tracks such as Silverstone. But the despite what the company says is a stronger construction, the teams were told to run the tyres at unusually high pressures – 26.5psi at the front and 23psi at the rear.
This compares with 23 and 20psi at the Austrian Grand Prix last weekend and 24 and 20psi at the Spanish Grand Prix last month.
As the session ended, Hollywood star Brad Pitt was preparing to take to the track in a modified Formula 2 car, the first race at which filming will take place for the new Apple F1 movie.
The Oscar winner, who has been practising at Silverstone in the lead up to the race, is playing a veteran racer called Sonny Hayes who returns to the sport to mentor a rising young star.
The film crew are operating out of their own garage at Silverstone and will continue their work at a number of races over the rest of the season.