Red Bull and Renault appear to be edging towards a split as early as next year.
The relationship between team and engine supplier has gradually deteriorated this year on the back of poor performances and Renault is now considering its own works team as Red Bull sounds out the possibility of a Mercedes engine deal. Initially both sides said they would honour the current contract until the end of 2016, but a report in Auto Motor und Sport suggests Red Bull is already looking to terminate the contract ahead of next season.
Asked by ESPN whether Red Bull would remain with Renault next year, team principal Christian Horner said: "As far as anything is certain in Formula One, we have an agreement with Renault and within that agreement there are certain obligations and parameters from both parties."
Pushed on whether he could say for certain Red Bull would be with Renault next year, Horner said: "What is certain in Formula One?"
The Red Bull boss has made it no secret that he sees the Renault power unit as the weakest link in his team.
"In order to achieve a championship or outright race-winning capability we need to have a significant step on the power unit. Obviously we need to make progress on the chassis and we are working hard to do that, but we need to close that gap down to our competitors."
Mercedes is believed to be top of Red Bull's list as a replacement engine supplier, but Mercedes boss Toto Wolff said formal negotiations would not start until the situation between Red Bull and Renault has been dealt with.
"We said and this is still the situation that we will not interfere into an existing relationship for many reasons," he said. "Legally we don't do this and it is not the way we approach business in general.
"We said, until that is resolved between the two parties, we will not even start any discussions because it hasn't reached that time and the complexities are quite large, with the many decisions to be made."