Red Bull wants Ferrari to give it 2016 specification power units, but the Italian team is understood to be reluctant because it is too late to ramp up its production schedule to accommodate more teams.

But there are now serious doubts over it being possible for Ferrari to make available even a supply of 2015 power units because of the time-scale involved.

With Red Bull owner Dietrich Mateschitz having made it clear that he will pull the plug on his F1 teams if they cannot get competitive engines, he could actually be facing a situation where there are no power units available.

Red Bull's options have now run out – with it ending its Renault's contract, Honda being unable to supply an extra team and Mercedes having said no.

A huge shock

Vettel, who won his four world titles for Red Bull, said he would find it hard to believe Mateschitz could pull the plug.

“It would be a huge shock,” said Vettel. “I think Red Bull has been part of Formula 1 for ten years and has supported it ever since.

“Of course, I have strong links to Red Bull and I know the team like the back of my hand. This is why I struggle to imagine them to pull out. I hope they will stay in the sport.”

Vettel admittted, however, that Ferrari is not in an envious position in deciding what to do – with Red Bull's future in F1 resting on what happens.

“I’m not the one to make the decisions. I think it’s no easy decision and to be honest I’m glad I don’t have to make it,” he said. “I’m comfortable in my role, being a driver only.”

Red Bull's desire not to accept anything but works parity with Ferrari is further fuelled by Ferrari looking set to make major architectural changes to its power unit for next year.

There are some suggestions the team could use its remaining engine development tokens to introduce a new narrower engine later this season as part of development work for 2016.

Horner says "everything is open"

Red Bull team manager Christian Horner was absent from the pitwall during FP1, instead holding lengthy talks at the RBR motorhome with Bernie Ecclestone and Helmut Marko.

"The circuit was a bit second-hand this morning so a bit more to be achieved off-track than on-track," Horner explained.

Despite stories emerging that the Ferrari - Red Bull deal might be off the table, Horner added: "There's a lot of discussion going on at the moment, I'm not gonna conduct our negotiations through you guys. Nothing is fixed, everything's open."