Red Bull concerned by Renault's conservative engine plan

Conscious of the new-for-2018 three-engine limit, Renault F1 managing director Cyril Abiteboul recently revealed his company wants to take a zero-risk approach to reliability.

But with Mercedes telling Autosport late last year that it is close to producing an engine that can deliver a power output of 1000bhp, Horner suspects the four-time reigning world champion team could be "mighty".

"It is a concern," when asked by Autosport for his response to Abiteboul's comments.

"If the headline figures Mercedes have quoted [are real] then the gap will only broaden.

"Renault have their own team now, they have their own demands they need to meet.

"Reliability has been a big priority for Renault over the winter.

"They have completed more mileage than they have done in this V6 era so they are coming into this year better prepared and hopefully that will allow focus to start to centre on performance.

"We're hopeful of seeing more performance and performance converging between engine manufacturers."

Horner added he "did not think it would be great" if Mercedes dominated F1 for another year.

"It just emphasises why engine regulations need to be clarified this year for 2021," he added.

"The problem is if we go past the midyear, then manufacturers will say there is not enough time for 2021 so there is a lot of positioning going on at the moment.

"It's crucial the commercial rights holder and the FIA come out with a clear positioning and regulations, particularly on the engine, by the middle of this year."

Last year, Renault was working to end its supply deal with Red Bull at the end of 2018 as part of the fall-out of Toro Rosso's divorce from Renault.

But Horner said 2018 was "not necessarily" the last year it would be supplied with Renault, which it has worked with since the start of 2007.

He added: "All things are open for 2019 onwards.

"We will play close attention to how things develop at Toro Rosso but there are no preconceptions as we head into the season."