Fernando Alonso is optimistic that Ferrari has taken a step forward with its upgrades for the Turkish Grand Prix, but felt he could not make a proper judgement about the car's potential today.
The former champion was only 11th in Friday practice at Istanbul, though he lost some time with mechanical issues.
"I think it's difficult to evaluate right now, because we've just finished practice," said Alonso.
"But the car felt good. It was okay this morning, okay this afternoon.
"We had some mechanical issues on my car, but nothing too worrying.
"Performance is difficult to evaluate after Friday - you never know what the others are doing.
"I think we made a step forward - but we need to see how big it was."
Alonso feels it is currently impossible to clearly evaluate the effectiveness of the upgrades.
"The improvements we've brought here are aerodynamic parts, so what you feel in the car is more overall grip," he explained.
"But whether it's down to the tyres or the track and everybody is feeling it, we don't know.
"I think Mercedes also improved a lot. They are quick. I think Renault will also be competitive. So it's tough. I think in two or three tenths you can be fourth, fifth or ninth.
"So we just need to do our best tomorrow, take the best potential we can out of the car."