Red Bull and their engine supplier Renault will reportedly split after the 2018 season.
The shock news emerged just as Honda's move from McLaren to the junior Red Bull team Toro Rosso was about to be also announced.
Some reports say that Renault are dumping Red Bull at the end of an often fractious relationship, while other sources say the energy drink company is happy to assess a potential 2019 tie-up with Honda or usher Porsche into F1.
Dr Helmut Marko told Auto Bild: "I cannot comment at this time."
The news of Renault's departure, perhaps to be replaced with the unreliable and uncompetitive Honda power unit, is making the Red Bull drivers nervous.
"Yeah, they obviously need to improve," Daniel Ricciardo said of the Japanese supplier.
"I'm sure there's a reason to [the move to Toro Rosso], and there's some faith they're going to get better, but for sure [Honda will] need to show up next year.
Teammate Max Verstappen, on the other hand, is already unhappy with his season at Red Bull, and now contemplating the final Renault-powered year in 2018.
"If this can happen, it's not until 2019," said the Dutchman when asked about a potentially Honda-powered Red Bull in the future.
"All I know is that next year I will drive a Red Bull car with a Renault engine.
"So first of all I want to focus on the beginning of the season and see how competitive we will be.
"It is also possible that next year the Honda engines will be very good. So I think we just have to wait and see how everything will turn out."
The 2017 season continues on Sunday with the Singapore Grand Prix.
