Mercedes has delayed the planned introduction of a new engine specification for Canada.
Toto Wolff announced days ago that "all the Mercedes powered cars" in the field will use the new engine in Montreal.
But now, it emerges that Mercedes has in fact delayed the planned introduction by one race.
"We wanted to use the second power unit this weekend, but a quality problem means we’ve moved it to the French grand prix," a spokesman said.
It is good news for Ferrari, whose championship contender Sebastian Vettel will use a new engine in power-hungry Canada.
And it’s also a crucial weekend for Renault and Honda, with the latter also introducing a new power unit that it hopes will convince Red Bull to make the switch for 2019.
Spanish reports say Honda has signed up a key engineer from Mercedes, Axel Wendorff.
"We are introducing an updated PU for this event, fitting it to both cars," announced Honda’s technical boss Toyoharu Tanabe.
"The updates are mainly to the ICE, focusing on improving performance."