Mercedes boss Toto Wolff says he doesn’t know the exact reasons for Valtteri Bottas’ Formula 1 power unit failure at the Eifel Grand Prix.

Bottas’ race at the Nurburgring was cut short after he suffered a loss of power on Lap 19.

It is Mercedes’ first retirement of the season and a rare power unit issue for the team.

When asked about Bottas’ failure, Wolff said: “We don’t know yet. We know that it looks like it was around the MGU-H but we haven’t found the root cause yet. We retired the car, not only because we wouldn’t have scored points but we wanted to damage the power unit.

“I think we should be fine. It’s important to understand what actually happened as we introduced new power units this weekend and there’s still six races to go so we need to get on top of the problem.”

Wolff saw his two drivers duel it out for the lead of the race on the opening lap.

Hamilton got the initial better launch and looked to have the move done on Bottas into Turn 1, but the Finn managed to get a superb run on the outside and reclaimed the position into the next left-hander.

Wolff admits he enjoyed the battle and is confident Bottas will bounce back from this latest setback despite now trailing Hamilton by 69 points in the race for this year’s championship.

“I enjoyed the racing between the two of them because I’ve never doubted that there will be any contact,” Wolff added. “These guys respect each other, they know very well what the boundaries within this team are.

“I think that Lewis braked a little bit late and had full lock, and that obviously pushed Valtteri wide but Valtteri, in true style as a rally driver, kept the foot down and deserved to preserve the position. I enjoyed that. In terms of the championship, Valtteri is, I just saw him before, if somebody’s resilient it’s him.

“We had a good chat. I said ‘sorry for the failure’ I believe that a two-stop that he said himself, would have been actually something that could have worked out to win the race but it is what it is. This is still a mechanical sport and today, it was us that let him down.”