Lewis Hamilton expects "a struggle" for him and his Mercedes team at the Hungarian Grand Prix after finishing a lowly 11th place in practice on Friday.
The seven-time world champion suffered damage to the floor of his car and had to abort his race simulation run, complaining that his car felt unstable on the Hungaroring circuit where he has won a record eight times.
"The car is a bit of a struggle today," said Hamilton. "It's crazy how much it swings from track to track. It's a bit loose and not doing what we want it to do -- so a difficult day.
"Nothing has changed on the car since last week and I'm the same driver, but for some reason the car is not working on this track.
"I didn't get to run at the end, as I sustained some damage to the floor, and after that it was a bit tricky for the long run. It's going to be a tough weekend, but we'll give it everything we have got."
Mercedes were only sixth fastest of the leading teams, a setback to their recent improvement which has seen Hamilton reel off four consecutive podium finishes, including taking second ahead of team-mate George Russell at last Sunday's French Grand Prix.
Russell, who was eighth after second practice, said it had been "definitely not our smoothest Friday so far," adding that it was puzzling for the team as after Friday's heat they were likely to face cool and wet conditions on Saturday.
"We were trying quite a few things with the car, using it as a bit of a test session, because to be honest you can try and optimise everything today, but there's no use in that at all for the rest of the weekend.
"So, even though it's been a very tough day, I think it's probably been a productive one."
He added that the team were "a little bit further away than we probably would have expected" but "all is not lost".