Toto Wolff has admitted that he has "no explanation" for the engine problem that saw Lewis Hamilton finish 10th in qualifying for the Russian Grand Prix.
The reigning world champion, who was quickest in the final practice session on Saturday morning, suffered the same system failure at the Chinese Grand Prix.
Hamilton's Mercedes teammate Nico Rosberg was among those to capitalise, taking pole to leave himself in a position to extend his 36-point lead at the top of the drivers' standings.
Sebastian Vettel of Ferrari took second ahead of tomorrow's race, but a five-place grid penalty puts Williams driver Valtteri Bottas on the front row in Sochi.
Asked about the engine issue, Mercedes boss Wolff is quoted by BBC Sport as saying: "It seems to be the same fault as in Shanghai, even though we changed all the parts, so we need to analyse that properly and especially what we can do for tomorrow.
"There is no explanation. It is a mechanical sport and sometimes you run into these really awful series and this is happening to Lewis at the moment.
"We are trying to push performance and if you push the boundaries you will reach a limit. We seem to be missing a bit in there and it is a very complex technology and we need to find out how we can avoid these things in future."
To make matters worse for Hamilton, he was also reprimanded by stewards for not rejoining the track in the right manner after running wide at Turn Two in qualifying.
