Red Bull and Toro Rosso are in talks with current engine supplier Renault as they battle to secure a power unit for 2016, Autosport understands.
It marks a turnaround after Red Bull last month decided to end its association with Renault - which dates back to 2007 - at the end of the season.
Renault, currently in talks to buy Lotus and create a works outfit, had also previously said it was no longer willing to supply engines.
Senior Red Bull figures have made repeated threats to quit F1 if it cannot find competitive engines for its two teams.
Red Bull boss Christian Horner has said it is up to him to convince owner Dietrich Mateschitz to stay, with efforts taking place behind the scenes to find a solution.
However, Mercedes has made clear it will not offer a supply, while talks with Ferrari have yet to come to fruition.
With time running out to find a power supply for 2016 because of the impact it will have on the build of next year's car, the door is open for Red Bull to continue with Renault, according to Autosport sources.
F1 supremo Bernie Ecclestone, meanwhile, has confirmed "everything is being sorted" as he plays his part in ensuring the grid does not fall to nine teams and 18 cars next season.
Despite recent claims from Mercedes non-executive chairman Niki Lauda that Mateschitz has lost interest in F1 Ecclestone said: "He knows what he's doing.
"He has never fallen out of love with F1. He just wants to be in a position where he can be competitive.
"And that's what will happen. He will be OK."
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