BARCELONA (Reuters) - Renault will hold Red Bull to a May deadline to decide what Formula One engine they will use in 2019, the French manufacturer said on Tuesday.

Britain Formula One - F1 - 2017 Renault Formula One Car Launch - The Lindley Hall, London - 21/2/17 Renault's Jolyon Palmer, Nico Hulkenberg, test driver Sergey Sirotkin and managing director Cyril Abiteboul during the launch Reuters / Alan Walter Livepic

Renault are supplying McLaren and Red Bull this year as well as their own factory outfit, but Renault Sport F1 managing director Cyril Abiteboul said going down to two teams would be no problem.

“We’ve always said that to be an engine supplier is a very bad business,” he told reporters during testing at the Circuit de Catalunya.

The Formula One sporting regulations stipulate that the four power unit manufacturers must inform the governing FIA in May of the preceding season which teams they have a supply agreement with.

Anyone without an agreement will be supplied by the manufacturer with fewest teams - which effectively means Honda since the Japanese company only supplies Red Bull-owned Toro Rosso at present.

Mercedes and Ferrari both supply three teams.

Red Bull won four titles in a row with Renault engines between 2010 and 2013 but the relationship soured with the introduction of the current V6 turbo hybrid units and an era of Mercedes domination.

It was strained almost to breaking point in 2015 and Red Bull, who have Australian Daniel Ricciardo and Dutch youngster Max Verstappen as drivers, then re-branded the Renault engines as Tag Heuer.

“We are not going to hang around forever,” Abiteboul said. “I know what (Red Bull team boss) Christian (Horner) is referring to when he says that he has options. He’s absolutely right. But one thing that is clear is planning.

“At the end of May there needs to be some clarity as to who is supplying which team. As far as we are concerned, that will be our deadline.”

The season starts on March 25 in Australia but Horner has expressed concern, despite his car being fastest when testing started on Monday, after Renault said they would put reliability before performance for the first few races.

Abiteboul said being an engine provider was an often thankless task but the rules, with a driver’s allocation reduced to three units from four, made reliability even more important.

“It’s a no-brainer that this is what you have to put as a priority,” he said.

“The key message is that the fact of being reliable opens up more options in terms of performance. The two go together. When you work on reliability, you actually work on performance also,” added the Frenchman.