Daniel Ricciardo's Red Bull is inspected by engineers

By Andrew Benson, chief F1 writer

Red Bull say they will pull out of Formula 1 if they cannot get a competitive engine or Audi do not join forces with the team.

Red Bull are frustrated with partner Renault's failure to master the hybrid engines introduced into F1 last year.

Motorsport adviser Helmut Marko said Red Bull were interested in doing a deal that would see Audi enter F1.

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

But he denied Red Bull had already been in formal talks with the German company, which is part of the Volkswagen Group.

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."

Like all teams, Red Bull have a contractual commitment to race in F1 until 2020. They also have a contract with Renault at least until the end of the 2016 season.

Marko's remarks are a reference to a power struggle taking place at the very top of the VW Group, which also has Porsche, Lamborghini, Bugatti, Skoda and Seat among its brands.

Helmut Marko has been rumoured to be in talks with Audi

Ferdinand Piech, who had led the German giant for more than 20 years, resigned as chairman last month.

The 78-year-old was a staunch opponent of any of VW's brands entering F1, partly because of his personal antipathy towards F1 commercial supremo Bernie Ecclestone.

Uncertainty continues to surround the senior management of Audi as a replacement for Piech has not yet been announced. His two nieces were appointed to the board to replace him and his wife, who resigned at the same time.

Senior sources in the German car industry believe Audi chairman Rupert Stadler is keen on an F1 entry, but that idea was vetoed in January by Piech.

The team had further trouble with their Renault engines at the Spanish Grand Prix last weekend. external-link

Reliability problems mean Red Bull driver Daniel Ricciardo has already used four engines this season - which is as many as each driver is allowed to use throughout the year.

Red Bull, whose other driver Daniil Kvyat has also suffered engine failures, know it is inevitable they will be hit by grid penalties for using extra engines.

Mercedes drivers Lewis Hamilton and Nico Rosberg, by contrast, have used only one engine for all five races so far.

Daniil Kyvat has used the maximum number of engines permitted in a season

Marko said: "I hope the reliability issues are solved pretty soon because it is really depressing how much we are losing on the straights."

He added: "Renault see the problems themselves and we have to try and find out these problems together. It is not only reliability, it is also that we did not run most of the practice sessions because of other issues. It is also a quality problem. "