Mercedes does not understand why it has been unable to find the Pirelli tyres' "sweet-spot" in Singapore this weekend, but has ruled out the tyre pressure limitations enforced by FIA.
For the first time this year, neither Mercedes is on the front row of the grid for Sunday's race after they both qualified over a second off the pace of Sebastian Vettel's Ferrari.
"The moment we put the car on the ground on Friday in FP1 we seemed to struggle and have gone backwards over the weekend," Mercedes boss Toto Wolff said. "There are a lot of factors which have an influence and we haven't really determined yet what the main contributor to that loss of performance is.
"I think it's a combination of the mechanical grip we have been able to extract from the tyre. The car hasn't changed and it's still a very good car aerodynamically and the engine hasn't changed."
Since the Italian Grand Prix, Pirelli's recommended tyre pressures - which are enforced by the FIA - have been upped for safety reasons, but Wolff said his cars were running higher than the limit anyway.
"None of the pressure levels set by Pirelli had any influence on our set-up, we were well within the limits. There is no explanation for the drop in performance on the car. It is just that we haven't been able to put the car in the sweet spot of the tyre and get all the matrices right - ride height, camber, torque, pressure, temperatures of the surface. There is so much influence. This is new.
"We saw also last year that it was the track where we had the least margin to all the other teams. Why that is, it is a very special track and very different. It has been a more difficult track compared to the others."
Lewis Hamilton, who qualified fifth, said he had never experienced such a drop in performance from one race to the next.
"I don't really remember another time in my Formula One career where something like this has happened and where we have not changed anything on the car and we are a second and a half down. I don't remember that every happening before. So this isn't a new experience for us, but I have no reason that it is going to continue for more races, it might just be track dependent."