Red Bull will make Renault wait even longer to find out if it intends to use the French manufacturer's Formula 1 power unit in 2019.

Renault boss Cyril Abiteboul is frustrated that the energy drink-owned team is stalling over its decision to potentially switch to Honda power.

"I do not understand their evasive behaviour," he said. "They want to wait until Canada, but on Monday after the race in Montreal there will be no revelations."

Actually, Red Bull boss Christian Horner says that the team will wait much longer than just Canada next weekend.

"It will be a month or so. End of June, beginning of July. It's the timeframe we've always talked about," he said.

"We want to compare the two engines in Canada," added Horner, amid reports both Renault and Honda will use upgrades at the Montreal race weekend.

"We'll get small updates in Montreal but we need to get the most out of them. It's very important to us."

Horner's biggest concern about staying with Renault is that Mercedes and Ferrari are always better in the crucial qualifying sessions.

"If I'm not mistaken, in the last six races the five fastest laps were ours," he said.

"If we get more power in the last qualifying session, there will be nothing stopping us from making the lives of Mercedes and Ferrari very difficult."

An hour before the Monaco Grand Prix, three senior Honda officials were seen exiting the Red Bull motorhome.

Renault's Abiteboul says that the French outfit would like to stay with Red Bull.

"We would like to continue with Red Bull if they give us a three-year warranty," he said. "Then we could have planning security, invest more and justify more resources."

Red Bull are third in the team rankings ahead of the Canadian Grand Prix next weekend.