Gearbox problems hindered Sebastian Vettel in Friday practice for the Austrian Grand Prix.
Vettel was fastest in FP2 in Austria, but it was a far from perfect day for the Ferrari driver after he struck gearbox issues in both sessions.
The German stopped on track in the morning after just four laps, before he managed to set a representative time.
He had a different problem in the afternoon, which compromised his session.
"We had an issue with the gearbox," he said. "Some of the sensors switched into alert mode and we slowed down.
"Obviously now we'll have a close look, we don't know yet what it is the problem, but it seems unrelated to this morning.
"It's a circuit where it's important to have a rhythm, it's a short lap. You need to get into the rhythm, and it obviously helps the more laps you do.
"Obviously we couldn't do as many as we wanted, but that's what it is. We have to go from there and see what happens tomorrow and especially on Sunday."
Regarding Ferrari's form relative to Mercedes, he added: "Difficult to say. Obviously they are always able to make a step overnight. Hopefully we can stick with them and put a lot of pressure on them tomorrow."