Red Bull is flirting with a change of engine supplier, according to reports on Wednesday.
Dr Helmut Marko has told Germany's Sport Bild that the reigning world champion team will assess the progress made by current supplier Renault at the time of its home Austrian grand prix at the Red Bull Ring in June.
"We have to decide on our future engine partner then," he said.
Honda is returning to F1 as McLaren's works partner next year, with Red Bull magnate Dietrich Mateschitz recently saying he did not want to simply be a "customer" of the Japanese manufacturer.
There might be another way.
Red Bull already has close commercial ties to Volkswagen, the German carmaker giant.
"Volkswagen is already in other racing series, with engines that are similar to formula one technology," said Marko.