The two players were once teammates and appeared to get on well when they were at Manchester United.
AC Milan took the lead in the game through Zlatan.
The Swedish legend then clashed with Lukaku just before half-time.
Both players squared up to each other before they were pulled apart. Lukaku was particularly animated and tried his hardest to confront his former teammate.
The altercation continued into half-time as Lukaku tried his best to get to Zlatan while they made their way to the dressing rooms.
Watch the moment again below…
Because there were no fans inside the ground, audio managed to pick up what the two players said to each other.
And the comments weren’t exactly pleasant, as you can imagine. (Transcript via Italian Football TV – @IFTVofficial)
Zlatan: “You are a donkey”
Lukaku: “Let’s go inside you b****, we’re gonna see”
Zlatan: “Call your mother, do your voodoo s***”
Lukaku: “F*** you & your wife you little b****”
As the two made their way into the tunnel, Lukaku said: “You want to speak about my mother you son of a b****? I’ll shoot you in your head”.
The voodoo commented is believed to be a reference to a story once told by Everton shareholder Farhad Moshiri.
He claimed that Lukaku turned down a new contract because of a voodoo message he got after speaking to his mother telling him to go to Chelsea.
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Zlatan later confirmed that comment is what made Lukaku lose it.
“He first argued with [Alessio] Romagnoli, then with [Alexis] Saelemaekers,” Ibrahimovic said, per the Daily Mail. ” intervened to defend my teammates and Lukaku attacked me on a personal level. I was shocked. We were even teammates at Manchester United.
“Lukaku has a great ego, he thinks he’s a champion and he’s really strong. But I grew up in the Malmo ghetto, and when someone comes under me with his head down, I put him in his place.
”So, I hit him in his sweet spot: his Mum’s rituals. And he lost control.”