Engine-maker Renault said it was considering quitting Formula One on Friday after its previously successful partnership with Red Bull descending into mud-slinging.
Managing Director Cyril Abiteboul said it was weighing up several options, including buying a team and walking away, a move which could have severe repercussions.
Renault is one of only four engine suppliers in F1, and Red Bull warned it could also be forced out of the sport if the French manufacturer leaves.
"I can confirm that we're looking at a lot of options, including heading out of Formula One," Abiteboul told journalists at the Malaysian Grand Prix.
"Honestly, if Formula One is that bad for Renault's reputation, if we see that we struggle with the current formula, if Formula One is not delivering the value that it costs to Renault.
"Bearing in mind that when you are an engine supplier you have no financial incentive to develop and to fund engine development."
Red Bull also threatened to quit F1 after this month's disappointing season-opener in Australia, when Daniel Ricciardo placed sixth and Daniil Kvyat failed to start.
Frustrated Renault and Red Bull traded insults after the race, with Abiteboul reportedly calling the team's chief designer a liar over comments about the French engine.
Abiteboul tried to play down the row, claiming he was misquoted.
"What goes on tour stays on tour. It's not what I said, let's leave that behind," he said.
- 'Worrying signs' -
Abiteboul and Horner pledged to work together, but they also traded some testy barbs as tension crackled between them at a regular F1 press conference.
"It's getting better -- so Cyril keeps telling us," said Horner, in response to a question about the Red Bulls' straight-line speed.
And Abiteboul shot back: "I'm not sure that Christian will confirm that there's a lot of Red Bull in the engine that was in Melbourne."
The Frenchman added that there wasn't "a lot of enthusiasm from the corporate offices" at Renault after the Melbourne flop.
But he said Renault could also decide to invest further in F1, including buying a team, if it decides it wants to continue as a "credible player" in the sport.
Toro Rosso, which also has Renault engines, is openly courting an offer from the French company with team boss Franz Tost calling it a "fantastic opportunity".
Red Bull and Renault dominated F1 between 2010 and 2013, winning the drivers' and constructors' titles four years in a row, before Mercedes hit the front last season.
Abiteboul admitted Renault had been guilty of some complacency as Mercedes took the lead with F1's new, hybrid engines and left the competition standing.
Horner said: "As with any company Red Bull reviews its return on investment -- is Formula One delivering for Red Bull as a brand?"
"And there are some worrying signs when we see races like we see in Melbourne. Hopefully that's one chapter in a long story, and there's a long season ahead of us."
Source: AFP