Red Bull’s engine supply situation has reached a “critical” stage according to team boss Christian Horner.

With Mercedes having already turned down an approach from Red Bull it’s now clear that Ferrari is now only offering 2015 engines, as opposed to the 2016 customer units that will be supplied to Haas and Sauber.

Matters are further complicated by the fact that Toro Rosso also requires an engine, and due to its lower level of resources the Italian team needs to finalise the design of its 2016 contender at an earlier stage.

“The current situation is quite critical, because as we sit here, we don’t have an engine,” said Horner. “The important thing for us is to have a first class engine. First of all we need to conclude our situation with our current supplier. But I think Dietrich [Mateschitz] has made the situation very clear.

Regarding the deadline he said: “We are already late, already very late. It was already difficult two weeks ago, so we’re very, very late.

“Toro Rosso are in a similar situation. Their timing is more critical than Red Bull Racing, even.”

Horner has suggested that Red Bull Racing’s staff would do something else if it pulls out of F1.

“Then we’re in a position where we can’t compete. Then for sure we’ll have to look at other activities. Milton Keynes is full of a lot of talent, and we would have to look at where we apply that talent.”