Red Bull has not ruled out sticking with Renault beyond 2016, if the French car manufacturer makes good enough progress in Formula 1 next season.
The Milton Keynes-based team has signed a one-year deal with Renault for next year, with its power units being rebranded under the Tag Heuer name.
Despite the team's relationship with its engine partner having fallen apart this year, Red Bull motorsport advisor Helmut Marko has said it is not impossible that they could remain together longer term.
In an interview with the Red Bull-owned website Speedweek, Marko confirmed a single-year contract with Renault but that beyond that was totally open.
"For one year only," he said, when asked to confirm the length of the deal. "We continue to hope for the alternative engine from 2017.
"The other option would be that Renault develops so well during the 2016 season that we can consider to continue working with them."
Marko said Red Bull was also encouraged by the fact that Renault has secured the input of engine guru Mario Illien to help with development next year.
"We will have Renault power units at the same level as the factory team," he said. "Mario Illien will co-operate with his Ilmor company as a consultant with Renault to help development.
"He does it on behalf of Renault in Viry-Chatillon."
When asked how optimistic he was that Red Bull would enjoy a better campaign in 2016 than it had this year, Marko said: "The concepts presented by Renault look good.
"Now they need to be implemented and respected in practice what they promise in theory. The question is how quickly that will be possible."
Marko also added that Toro Rosso would run Ferrari engines, although there has not yet been an official announcement from the team.