Ex-Ferrari president Luca di Montezemolo had already suggested last week that Red Bull-owner Dietrich Mateschitz wanted to lure Volkswagen-owned Audi into the sport or else he would pull out of F1.

Red Bull has struggled with its Renault engines this year, with sixth place as its best result so far.

Marko said there had been no formal talks with Audi, but insisted Red Bull would leave F1 unless it can be competitive.

"If we don't have a competitive engine in the near future, then either Audi is coming or we are out," Marko told BBC Sport.

"There are so many rumours. Officially there was no request or talks.

"The VW Group first has to sort out who will be the new chief of support, who will run the brand of VW, and when they have sorted all these things maybe then they can think about what they are doing in motorsport.

"I was on the phone but not to the people you think."

Ecclestone would welcome VW

Formula 1 supremo Bernie Ecclestone said he is trying to make sure Red Bull does not leave the sport, and admitted VW entering F1 would be a welcome move.

"They [Red Bull] won't leave. We want to avoid that," Ecclestone said.

"I can understand that, and I'm not happy about it either."

"It would be great if they [VW] came in."