Renault Sport managing director Cyril Abiteboul is adamant Red Bull will have to decide this month if they want to remain customers with the French manufacturer in 2019.
Talks have formally begun between the advisor to the Austrian energy drinks giant, Helmut Marko, and Honda over a possible engine deal, having been suitably impressed with the progress they have made since working with junior team Toro Rosso at the beginning of this year.
The Milton Keynes outfit claim they will not be pushed around and will wait until the summer before making their final choice but Abiteboul claims the situation this time is very different compared to the late switch from Toro Rosso to McLaren for this 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?"
According to the regulations, teams must specify to the FIA which engine supplier they intend to use the following season before May 15 and it is this deadline that Renault wants to apply to Red Bull.
"It's not that we want to be awkward -- there's no tactics -- but we simply must define the quantity," the Frenchman insisted.
"That's why it's in the sporting regulations, and what we discussed with the FIA regarding the 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."
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