Red Bull owner Dietrich Mateschitz has said that "at some point even we've had enough" of the engine supply predicament that shows no sign of ending.
Mateschitz spoke to Red Bull-owned Speedweek, and said he still has no concrete plan for an engine supply deal to either of his teams, neither Red Bull Racing nor Toro Rosso.
When asked if either or both will be in F1 next year, he replied: “I cannot give a definite answer to that question because we still don’t know if we will get an engine and what else is planned for the future.
“But at some point even we’ve had enough.”
Red Bull Racing’s Daniel Ricciardo tried the new-spec Renault engine last time out in Interlagos – seen as a step closer to the team running unbranded Renault units next year.
Team principal Christian Horner said that in Brazil his team needs to know in the next few weeks what engine it will use if it is going to make next year's first pre-season test.
“At the moment we are right on the limit to be at the first test,” he explained.
“The team in Milton Keynes have demonstrated their ability to work to massively tight deadlines, and I am sure we will be able to meet whatever targets we need to, as long as we come to a decision in the next couple of weeks.”
‘Alternative engine’ blow
Red Bull's hopes of seeing the independent engine plan it wants for 2017 were dented on Tuesday when the plan was understood not to have got the necessary support needed to automatically go through to the next stage of the governance process.
With one source suggesting the idea will need more refinement before it will have any hope of getting through, Red Bull may find itself needing to consider an alternative idea.
However, it cannot be ruled out that the FIA's World Motor Sport Council decides to impose the measure due to extraordinary circumstances.
The governing body's position is expected to become clearer on Wednesday.