Red Bull could make a surprise switch to Honda power next season, with the Japanese manufacturer having emerged as a serious option now for the Milton Keynes-based team.
With no 2016 engine deal having yet been sorted, Red Bull is continuing to try to find a solution needed to ensure it can stay in F1.
Mercedes and Ferrari have already ruled out deals for the team next year, and a potential reconciliation with Renault is thought to be unlikely due to the breakdown in their relationship, but there remains a chance the power units can be rebadged.
Although Honda had previously been ruled out, sources suggest that it is now back on the table, if the Japanese manufacturer can be convinced to expand its supply deal.
Red Bull could call on Bernie Ecclestone to help convince Honda on that front.
Honda has previously ruled out having any customer teams next year, because of the time-scale in getting more engines ready for 2016.
Motorsport boss Yasuhisa Arai has consistently said that the plan was only to supply McLaren next year, while a Honda spokeswoman said last month that a change of stance was unlikely.
"As Arai-san has said, Honda has no plans of supplying a second team next year, and this has not changed," she said.
"As Honda have always said since returning to Formula 1, we are open to supplying additional teams in the near future.
"However, as it is very late in the 2015 calendar year to make such decisions, it is unlikely that we will be supplying any other teams for the 2016 season.
"The combination of a new power unit and a new chassis will require additional development from both parties."
Any expansion of Honda's supply deals for 2016 and beyond would need approval from McLaren, but the team may feel that progress with the power unit could be helped if there were two teams running the engines.
Although Honda may not appear to be the most competitive option for Red Bull right now, the updated engine delivered at the Russian Grand Prix gave some encouragement that progress is being made.
So there may be a view that the company could make the performance steps needed this winter to become more competitive.