Red Bull Formula 1 chief Christian Horner would be "highly surprised" if Mercedes helped Honda get up to speed with its power unit for future seasons.

Since returning to F1 in 2015 as a power unit supplier, Honda has struggled for both performance and reliability, lagging far behind its rivals and leaving customer team McLaren at the foot of the constructors' championship so far this season.

Honda tried to make gains for 2017 by redesigning the layout of its power unit to reflect that of Mercedes, only for the alterations to result in more issues that have left McLaren on the back foot.

Speculation in recent weeks has suggested that Mercedes could be set to work with Honda to aid engine convergence in F1, with the FIA estimating that both Renault and Ferrari are already within 0.3 seconds per lap of the German manufacturer.

Speaking to the official F1 website, Horner was asked if there was any possibility Mercedes could work with Renault - Red Bull's much-maligned engine partner - given the manufacturers' relationship in their road car divisions.

"Not that I am aware of," Horner said. "And I would be highly surprised if the Honda/Mercedes thing were to happen.

"Honda has with Mario Illien, a very capable man who I think will be able to sort out the issues.

"And Renault and Mercedes? I think the problem element would be Red Bull."

Red Bull has been marooned in third for much of the season so far, trailing Mercedes and Ferrari, with much of the deficit to the leaders being put down to issues with its Renault power unit.

Drivers Daniel Ricciardo and Max Verstappen are eagerly awaiting the next update from Renault, which Horner estimates will be ready for the Canadian Grand Prix in June.

"It seems to be work in progress. They said it will be the third engine and it depends on the introduction of that engine," Horner said.

"Sure, we are keen to have it as soon as possible. We hope it will be Montreal. We are going to church every week to pray that it will happen as soon as possible."