Red Bull boss Christian Horner says the progress of Renault and Honda's respective engine upgrades in the lead up to June's Canadian Grand Prix will dictate the team's decision on 2019.
Red Bull is in the final year of its contract with Renault and it looks likely the pair will split, having seen its relationship deteriorate since the introduction of V6 turbo engines in 2014. The only alternative would be Honda, which took on the supply of Red Bull's junior team Toro Rosso for this season.
Renault previously warned Red Bull it would not budge on its deadline of May but Horner has other ideas.