Hamilton's Russian GP qualifying failure a 'freak' one - Mercedes

The reigning world champion encountered an identical MGU-H problem to the one that affected him at Shanghai when he headed out on track for the second time in Sochi Q2.

Wolff said Mercedes believed it had understood the problem in China so now plans to carry out further analysis.

"What happened today is a bit of a freak failure because it's a scientific assessment process," said Wolff.

"We had a failure in Shanghai which we understood.

"We changed the parts and here we go again, the same thing happens.

"So we need to find out if we have really identified the root cause of the problem.

"Beside that, the car was rock solid. It's a fast car, this weekend probably the fastest so far, and we've had these two unfortunate failures on the MGU-H."

Wolff said Mercedes has yet to decide on a plan of action, such as changing the engine. A decision is not expected before Sunday morning.

"There are many balls in the air at the moment to find out the root cause and what we can do," he said.

"Whether we need some bits from Brixworth which need to be flown in or not and what parts we exchange or not.

"I can't tell you precisely yet what we are going to do because I don't know."

However, Wolff confirmed it was not a problem caused by the driver.

"It's certainly not Lewis," he said. "We need to look at settings maybe on the MGU-H, any setting which could have an influence on the functionality of the power unit.

"We have eight power units out there, seven didn't have any problems and one had the problem twice.

"You need to turn every stone and looking at settings, because it happens in the same circumstances - in qualifying twice and on out-laps, not in the race so I wouldn't exclude any failure.

"But it's not something which is obvious because we would have found out. It's not the driver's fault, that's definite."