Valtteri Bottas says Mercedes' latest aero upgrade package may have disrupted the handling of its W08 Silver Arrows.
Both Bottas and team mate Lewis Hamilton were uncharacteristically off the pace in Friday's free practice sessions, ending the day 1.4s adrift from Ferrari's Sebastian Vettel.
The German outfit installed new aerodynamic components on its car in Malaysia, with changes centered around the W08's nose and the bodywork ahead of its sidepods.
"We did try some new aero parts today, so one answer may be that one of those parts didn't work as expected," explained Bottas.
"I suppose the new parts are quite a big step, but it didn't quite seem to happen. The team is reviewing everything and we need to make sure we have the right parts for Saturday."
Both drivers reported a general lack of grip and overheating tyres on Friday, the latter a direct result of the former.
"The guys are still looking at everything. Normally this track was supposed to be quite good for us, but we were definitively not quick enough.
"It was not like the car was terrible to drive, the balance felt good, but we were missing grip.
"Normally on Friday you can never be too happy but today we were not far off in terms of balance [between front and rear].
The bigger problem, what we need to find out, is why we're missing grip. We really need to find more grip, somewhere, somehow.
"We were sliding quite a lot, especially in the high-speed corners, and it was the same case in the wet, so we need to find out why.
"In this kind of track you put so much energy through the tyres that if you slide you overheat the tyres and then it's tricky."
Bottas and Hamilton are likely to run with different set-ups in FP3 as Mercedes desperately seeks a performance boost, not only to try and bridge the gap with Ferrari but also to keep up with Red Bull Racing.