The Haas and Alfa Romeo teams won't use Ferrari's latest upgraded power unit at this weekend's Spanish Grand Prix.
Ferrari will introduce its spec-2 engine in Barcelona, bringing forward an upgrade initially planned for next month's Canadian Grand Prix.
In combination with the new unit, the Scuderia will also have access to a new lubricant concocted by technical partner Shell.
Haas and Alfa, who both run Ferrari customer engines, will upgrade to the spec-2 engine at Monaco or in Montreal.
Haas boss Guenther Steiner cited logistical constraints for the delay.
"Last year we put it in before them, it was the opposite way around," Steiner said.
"Everyone said, 'Why do you that?' and now we are the other way around. So how should we do it?
"Doing it at the same time is always logistically very difficult for them so 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."
The fact that Ferrari uses a different specification of fuel than the US outfit is not viewed as a disadvantage by Steiner.
"It is just a decision we took," he added. "That is it, there is nothing behind it. It is a bit of a different spec and it is fine."
Gallery: The beautiful wives and girlfriends of F1 drivers
Keep up to date with all the F1 news via Facebook and Twitter
