Renault Sport admits it has 'missed targets' with its 2015 Formula 1 World Championship campaign as indecision over its future in the sport continues beyond the season finale.

Considered the weak factor in Red Bull and Toro Rosso's 2015 F1 efforts, Renault's difficulties in improving the V6 Hybrid power unit were magnified by its failure to show any notable gain with its much anticipated - and delayed - Brazilian GP update.

For the season-ending Abu Dhabi Grand Prix, only two Renault-powered cars cracked the top ten, with Daniel Ricciardo finishing sixth and Daniil Kvyat in tenth.

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For Renault, it was a disappointing conclusion to a disappointing season, which marks the first year its engine hasn't won a race since 2007.

"Fourth in the championship for Red Bull is no doubt hard to accept and we all share that responsibility. At Toro Rosso, the championship position may not be as hoped, but with more than double the points of 2014, it's been a strong year overall for them and we are proud to have worked together to achieve this.

"At the end of a very challenging season, both on and off track, I would like to thank everyone at Viry-Ch?tillon for their hard work. At the start of the year when we came under fire it would have been easy to lose motivation, but all have kept their heads down and kept development on track.

"We have not reached the targets we set for ourselves, but I hope this year will be seen as an aberration to our usual good form."

As it stands, Renault's involvement in F1 remains unconfirmed, with continued delays in announcing whether or not it will go ahead and purchase Lotus. Red Bull, meanwhile, it is set to run a Renault engine without the branding and take charge of its development.