Four-time Formula One world champion Sebastian Vettel said Ferrari are still unsure what caused his practice session to come to a grinding halt on Friday.
With 15 minutes remaining in FP2, Vettel was left pushing his car before it was towed away as Mercedes duo Nico Rosberg and Lewis Hamilton dominated proceedings, with Ferrari fifth and sixth respectively, more than two seconds off the pace.
Vettel initially stated the rear-left wheel was loose but the problem remains undiagnosed, according to the German.
"We don't know 100 per cent what happened. I felt out of Turn 4 that I lost drive, so I decided to stop," Vettel said.
"Obviously we don't want to take a risk at this stage, damaging the car or the engine.
"It's a shame because I would have loved to cover more laps, but that's what it is. It was incredibly important to do the mileage today and get the information on Friday, but it's even more important to make sure that the car is in good conditions for the whole weekend and for the whole season.
"Tomorrow I think that if you want to qualify as high up as possible you have to use the Supersofts. It's not a big secret. We saw that a lot of people were doing their homework today.
"As for me, I haven't done everything I could because we had to stop, but Kimi did a lot of laps, so it's still reasonable. Coming down to our rivals, I don't know what they did today. I think we can still improve for tomorrow. Hopefully we can be a little bit closer, so we'll see."