Renault and Pirelli are puzzled as to the cause of Jolyon Palmer's high-speed tyre blowout in Friday practice.
In the morning session, it was youngster Esteban Ocon at the wheel of the yellow car, but his rear puncture is said to have been clearly caused by debris.
Later, however, the cause of Briton Palmer's 300kph rear failure in the same car proved more difficult to diagnose.
"The tyre was completely destroyed," team boss Frederic Vasseur is quoted as saying by Auto Motor und Sport. "We don't know why it happened."
The report says that Pirelli does not believe either debris or the high forces generated by the Barcelona circuit caused the incident as the tyre was only three laps old.
Pirelli are reportedly investigating.
