Budapest - Lewis Hamilton admitted on Friday that he and Mercedes are hunting for an overnight solution to their performance problems ahead of Saturday's critical qualifying session for the Hungarian Grand Prix.
The championship-leading Briton, whose team-mate Valtteri Bottas said his car "was difficult to drive", said the team needed to "dig deep to figure out what changes to make".
They were fifth and sixth in the second practice led by title rival Sebastian Vettel of Ferrari on Friday.
"The Ferraris and the Red Bulls were quite quick and had a little bit more pace than us, so we've got some work to do tonight," said Hamilton, who has won a record five times at the Hungaroring.
"This is a tricky circuit and the tyres are overheating - looking after the rear tyres is the biggest issue.
"The temperatures today and the layout of the track - corner after corner after corner - made it really tricky for the tyres as there's no time for them to cool down.
"We will do our debrief and dig deep to try and figure out what changes we make - I hope we're able to find something tonight and that tomorrow is dry, so we can test whatever changes we make."
Bottas said: "It was not an easy day. The car was difficult to drive and I struggled to get laps together.
"This is a difficult circuit, you need to have a well-balanced car in order to get all the corners right and we need to get the car more stable.
"It is difficult to overtake here, so track position is very important and the less stops you can do is always going to be better. Red Bull and Ferrari are as quick as expected - it's going to be very close."