Sebastian Vettel's tire failure during the closing stages of yesterday's first day of testing in Abu Dhabi was the result of a cut in the rubber.
According to Pirelli's investigations, the failure on Vettel's right-rear tire on the approach to Turn 11 was caused by something the Red Bull driver picked up from the track.
Pirelli motorsport director Paul Hembery told AUTOSPORT: "It was a puncture – a cut. We didn't find anything [on the track], but looking on the tire there was quite a clear cut. It happens.
"The track is quite dirty now, it has been running quite a lot of cars. Most tracks where you get that amount of running in a short period of time, you can pick something up."
Vettel also suffered a second tire failure during this morning's running. Early indications suggest that the cause was the same.
Despite Vettel's problems, none of the other teams have suffered similar failures and Pirelli has not encountered any problems during its test running using the Toyota TF109.