Helmut Marko has revealed Red Bull will quit Formula One if the team cannot find a competitive engine for the 2016 season.
Red Bull have failed to win a race in a 2015 season dominated by the straining of the relations with engine supplier Renault, who have found it difficult to adapt to the era of the V6 turbo-powered unit.
Renault has faced much criticism as a result and, although they have agreements with Red Bull and Toro Rosso until the end of the 2016 season, the French manufacturer has said it is no longer willing to be an engine supplier in F1.
Furthermore Red Bull are reported to have requested an early termination of their deal with Renault as they seek a potential switch to Ferrari engines.
And Red Bull's motorsport advisor Marko told Sky Sports News: "The decision is done. If we don't have a competitive engine we will leave Formula One.
"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 [in the Italian Grand Prix] we were two seconds behind."
Marko was speaking on the same day that Red Bull driver Daniil Kvyat set the fastest time in second practice at the Singapore Grand Prix.
He added: "Today [Friday] we are ahead, but maybe that will change tomorrow, but we will be very near the front. As long as you don't have a power unit that which can compete it doesn't make sense."