George Russell suffered "catastrophic failure" in Canada confirms Mercedes technical boss, James Allison.

The Briton was battling teammate Kimi Antonelli, when, on Lap 29, he missed the second chicane and pulled to the side of the track, thereby allowing the Italian teenager to cruise to victory and extend his title lead.

Allison has now revealed the cause of the retirement, the reaction to which earned Russell a suspended €5,000 fine for an "unsafe act".

"It was a big weekend for us," admits Allison. "Key, because it was the weekend where we introduced our first major upgrade for the year and we were looking for it to be strong.

"It was, but a weekend that was otherwise extremely good from a performance point of view was marred by the disappointment we all feel for letting George down with the reliability of the car," he adds.

"On George's PU failure, it was an engine kill caused by a failure in the battery, which just suffered a catastrophic failure a third of the way into the race and brought George's race to an end there.

"We can see enough at the end of the race that the battery was fairly unhappy," says the Briton. "There's some heat damage there, and we'll have to figure out in the coming days and weeks exactly what caused that and put it right."