Christian Horner says he remains none the wiser over whether Red Bull will still be using Renault engines next season as he is yet to clarify the team's contract situation with the manufacturer, even if he believes a decision is now imminent.

Renault's intentions for the 2016 F1 season remain largely unknown beyond its now formally acknowledged interest in purchasing the Lotus team and reviving its role as a manufacturer entry, but there are conflicting views over how such a deal will be finalised.

However, while Horner has emphasised that Red Bull still has a contract with Renault - one that he is confident the French firm will honour if it has to -, he admits he is becoming frustrated with the time it is taking to come to a formal decision.

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"Obviously time is starting to press on now. We're now into September and everybody needs to know: What are Renault's plans for the future? I would have thought within the next two weeks we should all know what Renault's position is."

Should Red Bull move to get out of its Renault contract for 2016, its options appear limited to a customer supply from Mercedes and Ferrari. However, there has reportedly been opposition to the former from within Mercedes, while Ferrari is already potentially stretching its resources by supplying four teams in 2016 with the arrival of Haas F1.

Horner has previously said he expects Renault to continue prioritising Red Bull Racing as per its contract, regardless of whether it enters as a full manufacturer team in 2016.