Adrian Newey has acknowledged that his Red Bull cars will almost certainly continue to be powered by Renault engines next year.
The Austrian team is concerned about its horse power deficit that began amid the so-called 'engine freeze', with Mercedes and Ferrari pulling away in that area.
But technical boss Newey told Germany's Sport Bild that Red Bull is likely to stay with Renault.
"Where shall we go?" he is quoted as saying. "McLaren has stopped us from getting the Mercedes engine.
"So there's only Ferrari. But we ask ourselves: if we beat them, will we still have the same specification as the Ferrari team?" admitted Newey.
And although perhaps as much as 40 horse power down, Newey acknowledges that Renault "always respond to our requests".
He said the French marque "very strongly adhered" to the spirit of the engine freeze, developing its V8 engine less than its rivals.
"This means we now have a gap to Ferrari and Mercedes. And if Renault are not allowed to keep up, I can well imagine them withdrawing as an engine supplier," added Newey.