On lap 24 of 51, the McLaren pair came to blows at the first chicane as rookie racer Piastri re-joined the Monza track alongside earlier-stopping Norris in a dice for what was then 10th position.
With Piastri on the inside at the tight first apex, the front-right of the Australian’s MCL60 glanced his team-mate's sidepod. There was no major damage and both escaped punishment from the stewards.
Nevertheless, team boss Stella branded the incident as “unacceptable”. He said: “There should never ever be contact between two McLaren cars.
“There was a contact, which doesn’t fit the way we go racing at McLaren.
“What is important is to have clear parameters as to what you deem acceptable and what you deem unacceptable. It’s not an emotion thing, it’s just like you do with other things.
“You deal with racing in a similar way. This is very clear that for any driver, there’s something bigger than them. It’s the team.”
Stella added that McLaren did not necessarily need to take urgent action in response to the bash and considered whether Piastri had misjudged emerging on colder hard tyres.
The Italian continued: “I need to review. Like all things, we will do it calmly.
“There’s nothing that we need to do urgently. We will make the adjustments that we need.
“It’s always a little tricky when you leave the pits, especially on hard tyres.
“It could be that certainly, Oscar was trying to see where he could place himself so that he could keep the position.
“But on colder tyres, this could be slightly more difficult than he might have anticipated.
“We could absolutely conclude that this is just a little misjudgement.
“Both drivers were aware that there must be no contact between two McLarens and it was just an issue with the execution - we all have issues with execution.”
Asked whether McLaren’s undercut strategy for Norris had created the scenario, Stella said it remained inexcusable for drivers to ‘affirm themselves’ by placing the team at risk.
He said: “If the contact is due to the fact that there was pressure because of the undercut, then we have something to review.
In a race that ended with a clean Ferrari battle that was celebrated by both Scuderia drivers and team boss Fred Vasseur, Stella added that his duo were “free to race” also.
Stella said: “My role is to give them principles and a clear parameter within which they can race.
“This is what we want to see - it is exciting to see like the Ferraris today.
“In terms of how you stay within the parameter, it’s not for us to say because we are not the drivers. It’s actually within them to have the skill set to say, ‘the tyres are a bit cold, maybe I need to take more margin’.
“They need to appreciate that there is no way the line should be crossed.”
