Red Bull and Porsche are not yet ready to announce their likely works Formula 1 collaboration for 2026.
It had been expected that Red Bull's home race in Austria, and the only grand prix in a German-speaking country, would be the perfect venue for an official confirmation of the rampant paddock rumours.
But Dr Helmut Marko said Porsche cannot make any announcements until the delayed 2026 engine regulations are set in stone.
"It's realistic in the fall," the top Red Bull official told Kronen Zeitung.
It is believed the team's new 'Red Bull Powertrains' subsidiary will develop the internal combustion engine in 2026, with Porsche handling the electronic side.
"All I know is that the VW Group will get involved once the regulations are in place and that's not the case yet," Marko said.
He said the rules are basically now agreed "but Ferrari wants more modifications around the exhaust".
When asked when the negotiations will be complete, Marko answered: "Originally it was the end of June, more recently it was the end of July, but that's also quite difficult."
A second Volkswagen brand, Audi, is expected to launch a completely separate works F1 project by buying into the Sauber (currently Alfa Romeo) team.
Meanwhile, although Spa-Francorchamps (Belgium) and Paul Ricard (France) are in serious danger of losing their grands prix in Europe, Marko insists the Red Bull-promoted Austrian GP is safe.
"The Red Bull Ring is always among the best-rated grands prix and Red Bull also make up 20 percent of the grid," Marko said.
The 79-year-old admitted that other venues may offer "more money", but "it is very clear that traditional circuits will have to be retained".
"The Red Bull Ring is not in danger," said Marko.
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