Red Bull advisor Helmut Marko on Friday said the team will quit Formula One if it cannot find a competitive engine after its looming divorce from Renault.
Red Bull won four straight titles from 2010 to 2013 but they are in danger of being left high and dry after Renault vowed to stop supplying F1 engines.
"The decision is done. If we don't have a competitive engine we will leave Formula One," Marko told Sky Sports, refusing to comment about a potential switch to Ferrari engines.
"I don't want to go into details, but what's clear is we want a competitive engine, because with these regulations you saw at Monza (Italian Grand Prix) we were two seconds behind."
Marko was speaking after Red Bull's Daniil Kvyat and Daniel Ricciardo finished first and third in Friday's second free practice session for the Singapore Grand Prix.
"Today we are ahead, but maybe that will change tomorrow... As long as you don't have a power unit which can compete it doesn't make sense," he said.
Red Bull lie fourth in the constructors' standings after a disappointing season which their hierarchy has consistently blamed on its Renault engines.
The French company has now pledged to walk away from the long-running partnership and is attempting to form its own team by buying out financially struggling Lotus.
The row leaves Red Bull with Ferrari as their only credible engine-maker, with Mercedes ruling themselves out and Honda struggling to be competitive with partner outfit McLaren.