Ferrari's Spec 2 engine upgrade won't be made available to customer teams Haas and Alfa Romeo this weekend.
Ferrari has pushed forward the upgrade in the hope it can close the gap to championship leaders Mercedes, with Spec 2 originally scheduled to make an appearance in Canada in two races time.
However it will only be used by Ferrari's Sebastian Vettel and Charles Leclerc this weekend, with Haas and Alfa Romeo forced to wait until either Monaco or Canada, according to Haas team boss Guenther Steiner.
"Last year we put it [the upgraded PU] in before them, it was the opposite way around [to this weekend]," said Steiner.
"Doing it at the same time is always logistically very difficult for them so for one reason or another, depending on the upgrade, they ask us if we are OK and we are fine with it.
"In the end, they need to manage the engine and the mileage and all that stuff. We are pretty happy with what they have suggested. It hasn't been decided if we do it in Monte Carlo or Canada."
Ferrari's fuel supplier Shell is also introducing a new lubricant this weekend, but Steiner confirmed Haas have made the decision to continue using the same specification this weekend and doesn't believe it will have a major impact on performance.
"It is just a decision we took. There is nothing behind it. It is a bit of a different spec and it is fine," he added.
