Red Bull Racing boss Christian Horner says Renault is contractually obliged to prioritise his team next season, regardless of whether the engine firm follows through on a plan to purchase the Lotus team and return as a fully-fledged manufacturer entry.

Relations between Red Bull Racing and Renault - who won four consecutive F1 world titles together between 2010 and 2013 - have been strained since a change in the regulations introduced V6 Hybrid power units in 2014.

Though Red Bull has been a staunch critic of the current engine formula, Renault's failure to make up ground on Mercedes and, more recently, Ferrari has nonetheless pushed the association close to breaking point, with the French firm considering whether to continue supporting Red Bull or whether to go ahead and purchase an existing team - well-known to be Lotus - to go it alone as a full manufacturer effort.

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Despite this, Horner remains unconcerned about the potential of its engine partner shifting its primary focus elsewhere, insisting it is in its best interests to keep developing during the second-half of the 2015 season and into 2016.

"They [Renault] have no choice for themselves, they have to turn it around," he exclusively told Crash.net. "We really need to see a good direction in the second half of the year that will carry a development theme into next year.

"We have a very clear situation with Renault until the end of next year irrelevant to the choices they make next year. Renault is aware of that so I think the most fundamental thing for both us and Renault is to address and reduce the deficit to Mercedes and Ferrari power units.

"Whatever they do they need a competitive engine and we have an agreement that clearly states we are the premium team. Whatever they do doesn't really affect us."

Should Renault opt to go ahead with its buy-out of Lotus, Red Bull's engine options beyond 2016 - when its current deal ends - appear fairly limited, with none of the four available candidates able to offer the primary focus it is likely to seek.

Despite this, both Mercedes and Ferrari have publically stated they would be willing to offer a supply, while the Honda is also considered to be in the running once it F1 engine production unit is constructed in Milton Keynes, where Red Bull Racing is based.