Red Bull Team Principal Christian Horner believes that Lewis Hamilton has been "forced" to use a fourth engine at the Turkish Grand Prix, rather than the decision being a strategical choice from Mercedes.
Hamilton's W12 has been fitted with a fresh Internal Combustion Engine for the Istanbul weekend, so he will incur a 10-grid place penalty for Sunday's race.
"From what we understand [it was] more of a forced choice, rather than a selected choice," Horner told Sky Sports.
"Obviously you've seen that they've had issues with some of their other teams as well.
"It doesn't affect us and what we're doing, but it shows how tight and tough it is to get to the end of the season on three engines, [something] that neither of us have managed.
"Hopefully we can do it on four [engines]."
Hamilton leads Max Verstappen by two points in the Drivers' Championship with seven races remaining. Verstappen started at the back of the grid last time out in Russia, due to a new power unit, and came through the field to finish in second.
Mercedes appear to be the team to beat in Istanbul, with Hamilton topping both practice sessions.
Horner added that he would not be surprised if there are other "twists and turns" which could cause more grid penalties for either of the championship protagonists.
"You can do all the simulations and modelling you like, and then something variable happens," said Horner.
"There's no such thing as total stability of a situation like you have in a simulated world to the end of the year. There could be other twists and turns in this, let's wait and see.
"Obviously we've taken a penalty, we've got ourselves into a good position, we've taken the additional parts as well – the battery the MGU-K, the MGU-H.
"Lewis has just taken the Internal Combustion Engine, [which] obviously is less of a penalty, but it's still going to put a lot of stress on those other components to the end of the year."