Sep.6 (GMM/Inautonews.com) Renault has delayed the introduction of a much-anticipated performance upgrade for its 2015 power unit.

Earlier, the Red Bull teams were holding out for October’s Russian grand prix at Sochi, because Renault was planning to debut a new engine improved by trading in performance ‘tokens’.

But Red Bull team boss Christian Horner said at Monza: “When the upgraded engine will appear is TBC (to be confirmed).

“There’s nothing actually confirmed yet,” he reiterated.

The feeling is that, as Renault is locked in deep negotiations with Lotus about re-buying the Enstone team, the French carmaker is now more focused on 2016.

Germany’s Auto Motor und Sport claims that the Sochi engine will now debut two weeks later in Austin, improved to the tune of 4 tokens, or 0.15 seconds per lap.

F1-insider.com, a website run by German correspondent Ralf Bach, said Red Bull has been informed of the schedule change.

Daniel Ricciardo, however, said: “No matter what is promised to us, I will believe in more power only when I feel it in the car.”