Mercedes executive director (technical) Paddy Lowe says he's never seen anything like Nico Rosberg's FP2 tyre blowout but insists its "too soon" to say there is a safety concern with Pirelli's tyres in Belgium.
Rosberg topped both Friday practice sessions but made the biggest headlines at the end of the FP2 when he suffered a dramatic right rear tyre blowout as he approached Blanchimont at 305kmh. The tyre failure pitched him into a spin and Rosberg was lucky to stop short of the tyre barriers.
Replays from Rosberg's lap appeared to show a thread on the inside of the tyre come loose on the run down to Les Combes.
"There's different bits of video showing some sort of unravelling up to a minute before the actual catastrophic failure," Lowe told Sky Sports. "The big question will be what's initiated that."
Asked what could have initiated that failure, Lowe replied: "I don't know, I've never seen anything like that before. We simply don't know, we'll have to wait. We'll obviously take the tyre away and make sure the car wasn't a contributor to it in some way.
"[I've not seen it] in a way where it has started to unravel. I don't know whether you've ever seen a video like that ... Normally these tyres seem to build up much more quickly."
Pirelli was investigating the incident when Lowe spoke to the media.
Shortly before Rosberg's blowout in FP2, Kimi Raikkonen had reported blisters on his front set of soft Pirelli tyres. Rosberg's were 11 laps old when he suffered the failure.
"It clearly started from the inside shoulder, which is always the most stressed part of the circuit, and this is a tough circuit on the tyres. But let's not pre-judge what's actually caused it until we found out. Pirelli has imposed - particularly at this circuit where there have been a history of issues with tyres - some limits which were declared earlier this week for pressures and camber."
Lowe confirmed Pirelli can adjust the pressures if the failure is discovered to be from a quality issue.
Asked whether it was too early too say if there was a safety issue with the tyres, he replied: "Oh yeah, very much too soon."
After the conclusion of FP2 Pirelli confirmed it is investigating Rosberg's blowout.