On Friday it was confirmed that Mercedes has opted to give Valtteri Bottas another new internal combustion engine, meaning the Finn will have to serve a five-place grid penalty at this weekend’s United States Grand Prix. 

It marks the third penalty in four races for Bottas after switching onto his sixth ICE of the year, which is more than double the permitted allocation of components. 

Lewis Hamilton was also forced to take a grid penalty for changing his engine at the Turkish Grand Prix as Mercedes tries to contain a problem with its power unit. 

Speaking after first practice in Austin, Mercedes boss Wolff conceded the issues remain a real concern for his team and its customers, with Aston Martin’s Sebastian Vettel and Williams driver George Russell also taking new engines. 

"You see this year we are suffering with reliability, we go onto the sixth engine for Valtteri and this is not something we choose to do,” Wolff explained. 

“We’re trying to really get on top of the problems and we haven’t understood fully. I think we are a step closer now, so it’s not always that we are easy with having the engines. 

“We are hanging on for dear life in supplying all customers - that is not trivial.” 

In an earlier interview with Sky, Wolff had dismissed a theory suggested to him that the problem relates to “something to do with air valves deep in the engine” as "bullshit". 

And Wolff was keen to keep the exact cause of Mercedes’ reliability headaches private when probed again during his appearance in the press conference. 

“I wouldn’t want to disclose what it is for obvious reasons but it is always a concern,” he said. “I think when you look at Monza for example, Valtteri had to start from the back and we are losing points on the way. 

“We are trying to push the performance every year and this year we’ve come to a point where that has cost us points. But over the last seven or eight years that mindset has won us races and championships. 

“I would have hoped for fewer penalties and use less engines but this year it has really hit us hard and McLaren and Aston Martin were more fortunate in that respect. 

“We just have to take it on the chin and do the best possible job.” 

Wolff was equally tight-lipped on the prospect of Hamilton needing to take another new engine - and subsequent grid drop - before the end of the season. 

“I can’t say whether we will be taking one and what the percentage is but obviously the risk is still there,” he stressed. 

“What is difficult to evaluate is, do you want to pre-empt the situation and take another penalty and take the hit, or do you want to really run it and then possibly risk a DNF. 

“That is a discussion that is happening as we speak and we haven’t come to the right answers yet.”