Ferrari changed the chassis of Sebastian Vettel's car on Friday after failing to get to the bottom of problems he experienced in practice for what could be a title-deciding U.S. Formula One Grand Prix.

A team spokesman said mechanics had found nothing wrong with the car after the German complained the front felt "like jelly", and had therefore decided to change the survival cell as a precaution. He said no penalty would be incurred.

The governing FIA said stewards had agreed the car could be submitted for re-scrutineering on Saturday before final practice.

"I felt something was not right with the car so we came in a couple of times to check and then go out to double and triple check. We are looking into it to try to see something," Vettel had said after second practice.

Vettel is 59 points behind Mercedes' Lewis Hamilton with four races remaining.

Hamilton, who was fastest in both practice sessions for a race he has won four times in the last five years, can secure his fourth championship if he beats Vettel by 16 points.