Mercedes driver George Russell lost 0.508 seconds to team-mate Kimi Antonelli in Belgian Grand Prix qualifying at Spa. The gap was mainly in straight-line speed despite changes to brakes and driving style. Both Russell and the team now believe a car issue is responsible.
Russell said he had initially convinced himself the deficit was down to his driving technique.
"We thought it was in the driving style and technique, but we've finally concluded it's not," he said after qualifying.
"There's a serious issue at play here and the team are working hard to resolve it."
Team principal Toto Wolff said Mercedes could not explain the straight-line deficit of a couple of tenths.
"We've literally left no stone unturned," Wolff said. "Is it the power unit, that Kimi has a brand new power unit and this makes a difference?"
Russell added that he felt powerless watching speed drop on the straights even at full throttle.
