The signs are growing stronger that Red Bull is preparing to switch to Mercedes-Benz power for next season.
Now team boss Christian Horner is quoted as saying by Bild newspaper: "We have several options (and) Mercedes is one."
In a separate report, in the Austrian newspaper Salzburger Nachrichten, Red Bull's motor racing advisor Helmut Marko also raised the prospect of an engine change.
"There are good arguments both for extending with Renault and for changing to Mercedes," he said. "By the end of August we want to know."
Vettel's two engine failures at Valencia, for which Renault apologised, were on top of two additional failures earlier this season, Marko confirmed.
"Those are facts that one must consider," he acknowledged, "as well as the fact that all of the drivers with Mercedes this year have had no problems."