The problem led to suspension and gearbox damage, as confirmed by a Mercedes statement.
This forced Mercedes to change Hamilton's gearbox, which was being used for the fourth weekend of its run of five, leading to the penalty.
Pirelli's conclusion is based upon its intial analysis of the tyre, along with the fact that Giedo van der Garde suffered a similar problem.
"Van der Garde was following and his rear tyre had a 10cm cut through it, a very aggressive cut that could only have come from a bit of metal," Hembery told AUTOSPORT.
"We are assuming that there was a piece of metal on the track that got into the suspension, the wheel, the brakes and that has caused us to lose the tread.
"It didn't deflate the tyre as the structural part was still intact and whatever it was went on and did van der Garde's tyre as well.
"That's all we can say at the moment."
PIRELLI KEEN TO RETRIEVE DEBRIS
Hembery confirmed the metal debris caused the tyre to overheat dramatically. This led to the loss of the tread.
"It has sent it into a massive overheat and we are trying to look at the telemetry to understand it," he said.
"We have a lab here, so we have some idea and can see some patches of overheating on the tread that has caused it to go well over 200C, which is rare and strange."
Hembery added that, as is routine, Pirelli personnel were due to walk the circuit after track activity had finished in an attempt to find the debris.
"We will go out and look as our guys always do a track walk," said Hembery.
"We are not overly concerned as it's just one of those racing things."