Williams and the FIA suspect that a loose drain cover caused Rubens Barrichello's high speed crash during the Monaco grand prix.
The team's technical director initially diagnosed a rear suspension failure.
"We have a good idea which part is suspect, but to be completely sure, we need to await the results of materials tests back at the factory," Sam Michael said earlier this week.
Germany's Auto Motor und Sport now reports that FIA experts conducted an investigation and now think a loose drain cover damaged the left rear wheel.
Another loose drain cover in the first sector of the famous street circuit last Sunday caused a short safety car period.
Barrichello's chassis and engine were not damaged, but the magazine said the Cosworth unit will as a precaution only now be used during Friday practice sessions this year.
The gearbox was also not substantially damaged, but Grove based Williams has decided to replace it anyway.
The sister FW32 of Nico Hulkenberg also crashed heavily in Monaco, meaning that both cars will have to use an older specification front wing in Turkey next weekend.