Sebastian Vettel has no doubts Mercedes did not show its true pace in Friday practice for the Singapore Grand Prix, and expects the team to raise its game on Saturday.
Lewis Hamilton finished down in fourth position in second practice, while Mercedes teammate Nico Rosberg wound up seventh.
Ferrari driver Vettel showed strong pace - especially over long runs - and was fifth, with teammate Kimi Raikkonen up in second.
"It's always difficult to predict after Friday, but I think it was a good day for us," said Vettel.
"The car seems to work and I think we can still improve.
"Obviously the Mercedes will be quick. I don't know what happened to them today, they looked a bit slow.
"But I'm sure they will change it for tomorrow. We know some of the Mercedes team usually they don't show everything on Friday."
Vettel admitted he was not too pleased with his short-run pace, and reckons he needs to improve it for qualifying tomorrow.
"I was not entirely happy with the short runs I had, so I think for qualy we have to improve a bit. For the race it looked quite okay, the pace seems to be there.
"But it's Friday, so we should keep our feel on the ground."