Red Bull tech chief Adrian Newey says the team now looks set to be forced out of Formula 1 after claiming its relationship with Renault is "terminal".
The Milton Keynes-based team is facing an engine supply crisis after both Mercedes and Ferrari refused to agree to a deal to provide power units for the four-time champion outfit.
Red Bull, which was set for a divorce from Renault after a disappointing season full of criticism towards the French manufacturer, suggested over the Russian Grand Prix weekend that continuing with Renault was still a possibility.
There's been too much of a marriage breakdown, so we have no engine.
But Newey said on Monday that it would be almost impossible for Red Bull to stay with Renault given the state of their relationship.
"Unfortunately, our relationship with Renault is pretty terminal - there's been too much of a marriage breakdown, so we have no engine."
Newey added that Red Bull needed Renault to get much stronger, but said he was unsure if the French car maker could make that happen.
"Improvement is needed, but there has been no clear direction on how to achieve that," Newey added.
"Red Bull should not be put in a position where they're only there to make up the numbers."