Works drivers Lewis Hamilton and Valtteri Bottas received the new unit at Spa, and thus have enjoyed the benefit of it at the two most power sensitive tracks on the schedule.

Green says that Force India and Williams were originally told that they would also have the upgrade from the Belgian GP, but manufacturing issues led to a delay.

Mercedes always treats both customer teams equally, and thus provides them with new units at the same time.

Both teams have now been told that they will get one engine apiece for Singapore, creating the additional complication of each team deciding which of their respective drivers gets to use it, inevitably leaving the other at a performance disadvantage.

"I think we're confident that we'll get to the end of the year without penalties, all things being equal," said Green.

"Are we happy that we're one power unit less than the works team? No, we're not. We'd rather be in their situation, to be honest.

"It's a performance upgrade, and given that these were the two most power sensitive tracks during the season, these were the two races where we would have really liked it."

Green said it was "unprecedented" for Mercedes to provide only one example of an upgrade to each customer team.

"One in Singapore is what we're promised at the moment. We were originally told we would get it in Spa. There's some disappointment, should we say.

"It's always useful having more horsepower, that's for sure, so it would have been nice to have had it at the two most power sensitive tracks that we go to."

Green said it wasn't a question of Force India missing out on any advantage Mercedes have gained by introducing the works engines before the new Monza oil burn rules came into force.

"We don't see that as a big issue. The latest power unit we're told is well within the new oil consumption limit. We're taking the same hardware, after the cutback in the oil consumption. We would expect it to be compliant, and it is."

Force India COO Otmar Szafnauer explained that Mercedes had been cautious in releasing the new engine to the customer teams because of reliability fears.

"It's never happened before," said Szafnauer of the prospect of only having one at the next race. "Normally you'd expect to get two. They're still working hard on getting us two. It could very well be that two happen before Singapore. But they can't be sure that happens.

"They had some manufacturing quality issues where they're not confident in giving us the new engines from a reliability standpoint."

The situation adds an intriguing twist to Sunday's race and the prospect of another battle between Sergio Perez and Esteban Ocon.

Szafnauer confirmed that usually the driver ahead in the championship – currently the Mexican – would get any new parts.

However, he hinted that the drivers also have to behave themselves in the Monza race or risk forfeiting that opportunity, even if they finish the weekend in front.

"In the past it's no secret that our rules of engagement, and most teams do the same, is that the guy ahead in the championship gets the one that we have," said Szafnauer. "It will be who helps maximise the team's points that gets it."

"We have rules of engagement that define where new parts go," said Green. "And we'll follow the rules."