Sebastian Vettel looks set to face at minimum ten-place grid penalty at the US Grand Prix later this month as Red Bull wrestles with lingering engine worries.

As well as battling against the superior Mercedes powerplant throughout the 2014 F1 campaign, the reigning world champions have also had to contend with less than stellar reliability and, despite things improving as the year has gone on, Vettel was using the last of his five-engine allowance at last weekend's Russian Grand Prix.

Now out of title contention, and with Mercedes having sealed the constructors' title in Sochi, Vettel's options are a little more open, but team boss Christian Horner believes that RBR will bite the bullet at the Circuit of the Americas.

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"We'll have to look after what happened [in Russia], but the reality is that Sebastian will take a sixth engine in Austin, because it's inevitable that he'll have to use it," Horner confirmed, "I don't think this engine can go too much further so the reality is that, in Austin, he'll have a sixth engine usage."

The extent of Vettel's penalty will become more apparent once Red Bull and Renault have had the chance to inspect the wear and tear on the unit he used to finish eighth in the inaugural world championship visit to Russia. Should he merely require new components, the German would pick up a ten-place grid demotion, but an entirely new power unit would bring greater censure, culminating in a potential pit-lane start.