Sebastian Vettel says Pirelli are investigating the cause of his blowout in second practice at Spa as he has no idea what went wrong.
Having hit the front of the timesheets on Friday afternoon, the Red Bull racer ventured out for another run on the medium tyres.
However, nine laps in he suffered a blown right rear, sending him limping back to the pits with strips of rubber flailing from the tyre.
The failure raised concerns in the paddock as the teams are already using the revised Pirelli tyres, which were introduced after a spate of blowouts at the British Grand Prix.
Speaking about the failure, Vettel said: "We don't know what happened when I got the puncture in P2.
"We lost the rear right, very suddenly, so we need to have a look - Pirelli is working on finding out why it happened.
"Other than that, it was a positive day."
The reigning World Champions, who holds a 38-point advantage over Kimi Raikkonen in the Drivers' Championship, went on to finish the day fastest, 0.059s up on his team-mate Mark Webber.
"This morning was tricky with a few rain drops and the track was slippery; it's a lot colder here than Hungary, but that's Spa and part of this circuit.
"This afternoon, we had stable conditions and both of us seemed happy with what we had."
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