Red Bull Racing boss Christian Horner says he remains optimistic a solution will be sought to ensure the team remains in Formula 1 next season, despite its dwindling engine supply options.

Following reports that Ferrari has withdrawn its offer to Red Bull over a disagreement on the specification it is willing to offer a rival team, the four-time title winning team's hopes of getting on the grid with the engine it wants has been dealt a potentially critical blow.

As a result, with five races of the 2015 season remaining, Red Bull owner Dietrich Mateschitz's original threat of withdrawing the company from the sport altogether now appears increasingly plausible.

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However, with the crises deepening over the course of the Russian Grand Prix weekend, Horner says measures are being taken to source a solution - including discussions involving Bernie Ecclestone -, which he confirms potentially includes a reconciliation with Renault since its 'divorce' hasn't been finalised yet.

"As we stand here nothing is fixed," he told Sky Sports. "We're working on lots of different scenarios. Bernie's actively involved as well and is very keen to find a solution and we need to. This team is too good not to be involved in Formula One and there is an awful lot of staff members, their futures depend on this decision so it is important we make the right one.

"I believe we'll find a solution. We need to, and I believe we will find a solution and hopefully one that is right for the team for the future.

Discussing the possibility to reviving its deal with Renault, Horner is cautious about the prospect since it remains in the dark over whether it will go ahead and purchase Lotus to reform its full factory effort or also exit the sport.

"Nothing is officially finished with Renault. There's a lot of speculation. It's difficult to envisiage we go forward but this is Formula One and nothing is impossible. We're still waiting to hear what are Renault's plans for the future -- are they going to buy Lotus, are they going to stop themselves? Everything is particularly in the air."

Meanwhile, Toro Rosso could still go ahead and use Ferrari engines after the Italian firm revealed it would still be interested in supplying the Red Bull sister team with a specification similar to that offered to Sauber and Haas.