Williams' hopes of having the latest version of their cars ready for Sunday's Turkish Grand Prix have been dashed by a lack of manufacturing time.
New parts had to be constructed for the cars after Rubens Barrichello and Nico Hulkenberg both crashed at Monaco.
"All of the items that needed replacing have been, apart from the front wings which require more time," said Williams technical director Sam Michael.
"As a result, we have to revert back to a previous specification for Turkey."
The F1 team is hoping to have updated cars ready for the Canadian Grand Prix on 13 June.
Michael is hoping to see a performance boost from engine provider Cosworth at the Istanbul circuit this weekend, while the cars will also have new brake ducts and mechanical changes.
The former champions, whose last drivers' and constructors' title came in 1997, are currently languishing in seventh place with eight points from six races.
German Hulkenberg went into the barriers in the tunnel at Monaco early on in the 16 May race, while Brazilian Barrichello crashed out in lap 31.