Andrea Beretta, 49, head of the "curva nord" (north end) ultras football supporters said he stabbed fellow Inter fan Antonio Bellocco, 36, after he had shot him in the leg with a firearm, his lawyer and Italian media reports said.
Beretta will be questioned in his hospital bed on Wednesday evening by a prosecutor, his lawyer Mirko Perlino told AFP.
The two men had an altercation as they rode together in a car on Wednesday morning outside a sports centre in the Milan suburb of Cernusco sul Naviglio.
Perlino told AFP that his client, acting in self-defence, stabbed the victim in the throat.
Beretta, who has been convicted several times for violence and drug dealing, became head of the Inter ultras after their historic leader Vittorio Boiocchi was assassinated in October 2022.
According to press reports, Bellocco is the heir of a powerful 'Ndrangheta crime family from Calabria, and has been condemned in the past for organised crime activities.
The prosecutor assigned to the case is Paolo Storari, who specialises in organised crime and who has led investigations into Boiocchi's assassination and into the mafia's infiltration of hardcore Italian football supporter groups.
