Williams identified late on Friday irreparable damage on Robert Kubica's FW42 chassis that forced the team to break F1's curfew to build up a new car for the Pole.
Kubica's FW42 was fitted with a new upgrade package but running was compromised at the outset in FP1 when the Williams lost a piece of bodywork.
Preparations at the end of the day revealed a damaged components that could not be repaired at the track, thus forcing the team to build up the team's spare chassis for Kubica.
However, the change will not entail a penalty for Williams as teams are allowed to break the curfew twice over the course of the season.
Between Kubica and teammate George Russell, Williams was able to complete its testing of new parts on Friday, and both cars should run the new-spec package on Saturday.
"We’re definitely looking forward to putting a bit more performance on the car but today it’s really difficult to know what the improvements were, as it was difficult to get a clear back to back comparison," Russell explained on Friday.
"The first signs seem relatively as expected."
Williams wasn't the only team to undertake a chassis change, with red Bull Racing also replacing Pierre Gasly's RB15 cell following the Frenchman's heavy crash at the end of FP2.