Renault's F1 MD Cyril Abiteboul has confirmed that Renault have put an offer on the table for Red Bull for next season.
Last year Red Bull tried to end their partnership with Renault but with none of the other suppliers willing to power them, they signed a one-year deal with the French manufacturer.
Running TAG-Heuer branded Renault engines, Red Bull have already achieved one podium result with Daniil Kvyat P3 in China.
As yet, though, there is no deal in place for next season although Abiteboul says Renault have made an offer.
He told Motorsport.com: "I think you can say that Red Bull has an offer.
"Frankly if you had asked me this time last year I would have been absolutely unable to answer accurately. It's not exactly the same situation, but it's also quite difficult to bet on a potential outcome from commercial discussions in this environment, which is F1.
"What I can observe is the relationship between Renault and Red Bull Racing is better. It has improved, on the back of the improvement of our product.
"I would hope and expect that if we continue to demonstrate that the product that we deliver can be improved, and can become also the type of engine that you need to be fighting for podiums and even championships, that there will be a mutual interest to continue."
He added: "There is an obvious relationship that can continue. If that principle is agreed, which is not the case now, then it will be about agreeing the figures.
"Red Bull is absolutely more than welcome to remain a customer of Renault. To be more specific, it's my wish, my desire.
"Now we need to deserve it from a technical and competitive perspective, through our product. It's what matters to Red Bull, and actually the test where we run the new spec is coming at just the right moment.
"It's just a bit late for May 15, but that's actually the point of making an offer prior to having an agreement. Red Bull have a binding offer from us."
Renault will trial their upgraded power unit at next week's post-Spanish GP test with the intention of running it at the next grand prix in Canada.