Lewis Hamilton is hoping Mercedes can "find our bearings" overnight after a lacklustre display from the Silver Arrows in the first two practice sessions in Malaysia.
Mercedes were off the pace in mixed conditions in FP1, but that story continued when the track dried out for FP2 in what is supposed a circuit that suits their W08 car.
However, Hamilton could only limp home in P6 in FP2, with even Fernando Alonso finishing higher in his McLaren-Honda.
"It's been a very difficult day," said Hamilton.
"I've been struggling with the car today, so we have to review and try to understand where we have gone wrong with the balance.
"We're hoping that we're able to find our bearings overnight and regroup for tomorrow."
Valtteri Bottas finish a place further down in P7 and believes qualifying looks a tall order at this stage.
"Those were obviously tricky practice sessions," Bottas said in his assessment.
"We had quite limited running because of the rain in the morning. I also had a bit of an off in FP2 that cost us some time, we lost a few laps because of that.
"We're definitely lacking some performance, it seems like Ferrari and Red Bull are very strong, so we have some work to do if we want to be on the front row tomorrow.
"The car balance itself didn't feel too bad; it's just a question of overall grip.
"The key area we are going to need to focus on tonight will be getting the maximum out of the tyres over one lap."