Renault could quit Formula 1 if the sport does not allow in-season engine development next year, Red Bull team boss Christian Horner says.
Renault, which supplies engines to Red Bull and Toro Rosso, admits it cannot catch Mercedes and Ferrari this year.
Limited in-season development is permitted in 2015, but has been closed off again for next year.
Horner said a failure to open it up would be "almost waving goodbye to" Renault.
Renault has a contract with Red Bull and Toro Rosso until the end of 2016.
Renault Sport boss Cyril Abiteboul said: "There will not be a future for Renault in F1 if we do not have a competitive engine."
When the current turbo hybrid rules were composed, the intention was that in-season engine development would be banned to keep costs under control.
Ferrari spotted a loophole that meant limited development has been allowed this season but governing body the FIA has closed it off by rewriting the 2016 rules. Manufacturers must submit all their performance improvements by 28 February next year.
To change this position would require unanimous agreement from the other teams and for now Mercedes are reluctant to agree.
Asked if he thought Mercedes would change this position, Horner said: "They don't have to obviously but it is at a precarious point in terms of Renault's commitment to the future.
"If F1 can afford to lose an engine manufacturer, stick to 28 February."
Abiteboul said the company was debating whether and in what form it should stay in F1 beyond the end of its contract with Red Bull in 2016.
Renault has the option to buy a team - with Lotus the favourite - stick with Red Bull as its works partner, or pull out all together.
Abiteboul said no decision had been made and "everything is open".