An uncompromising Renault has put Red Bull up against the wall, insisting it will require a decision by the Milton Keynes-based outfit about its 2019 engine deal by May 15.
Red Bull is pondering a choice for next season between extending its supply deal with Renault, its partner since 2007, or switching to Honda, but the decision is anything but a simple one.
On the one hand, Renault is a known quantity, albeit one with which Red Bull has endured a "roller-coaster relationship" as team boss Christian Horner recently put it, while Honda - Toro Rosso's current partner - still faces an uphill battle to bridge the gap with rivals Mercedes and Ferrari.
Red Bull formally initiated talks with the Japanese manufacture in Azerbaijan, and the pair are set to pursue their discussions next week in Spain.
However, engine manufacturers must confirm to the FIA their customer plans for 2019 year by May 15, although the deadline may be extended by the governing body following an engine manufacturer's demand.
But Renault's Cyril Abiteboul is determined to enforce the specific point in time, leaving Red Bull just ten days to choose its engine partner for next season.
"We have to [stick to it]," Abiteboul told ESPN.
"We have to for a very simple reason, which is that we need to order parts.
"The problem is that people tend to amalgamate what happened last year when we changed very late our customers, but we only swapped customers.
"So actually we decided to allocate, to deviate, engines that were produced for Toro Rosso and to make them available for McLaren, but the parts for those engines were already ordered.
"I have to order now, the longest lead time items for next year, so what do I do: three or two?"
Abiteboul denied he was maneuvering to purposefully put Red Bull under pressure.
"Frankly, I discussed that question with Red Bull on a regular basis. It's not that we want to be awkward -- there's no tactics -- but we simply must define the quantity.
"That's why it's in the sporting regulations, and what we discussed with the FIA regarding obligation of supply from suppliers to the customer teams, we agreed on the deadline of May simply because that's the life of the project.
"Red Bull will have to cope with it."
Should Red Bull decide to no longer rely on Red Bull to power its cars next year, Renault would be perfectly content to work with just McLaren as its single customer.
"It's important to have one customer -- I would not want to lose our two customers, really not, but that's also one of the reasons why we've done what we have done with McLaren, which is to have a long term contract with them until 2020," added Abiteboul.
"We are already in discussions with McLaren with what could happen beyond that point because there is a general feelings that we can achieve great things together.
"But, frankly, it's not a problem from moving from two customers to one customer."
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