Kubica was apparently under consideration, along with Sebastien Buemi.

According to Germany's Auto Motor und Sport however, the Pole's management team is excluding a one-off return because it would imply the reimbursement of a huge lifetime insurance payout Kubica received for being permanently unable to race in F1.

While a full-time return would likely be financially viable, Rosberg insists that Toro Rosso's one-race opportunity would be too great a risk for Kubica. "If you are thrown into deep water in a strange car without a test, you can only lose," said the German. "It is better to keep going for the Williams opportunity."

It has been mooted that V6 turbos with two electric motors (MGU-H and MGU-K) and that there will be many standardised parts to try and keep the costs under control for everyone.

As for the budget cap, it is being reported that it could be introduced in time for 2019 and that costs will be reduced on a gradual basis in order to help teams adapt to the new set-up.