Mercedes boss Toto Wolff has revealed that Valtteri Bottas’ engine blow-out in Spain was down to a defect never seen before at the Silver Arrows.

Bottas had to switch back to an old engine at the Circuit de Catalunya after a water leak was discovered when fitting in a new power unit.

The Finn had to retire from the race, but not before holding up Sebastian Vettel, because of an issue with the turbo and Wolff has said that the new problem is keeping everyone at Mercedes on their guard.

“It was painful to lose 15 valuable points with Valtteri retiring from P3,” said Wolff via the official Mercedes website.