Mari, who is on loan at Italian side Monza, was one of five people stabbed at a shopping centre earlier on Thursday. He was understood to be taken to a hospital in northern Milan.
Police initially said there had been six stabbing victims but later said the sixth person was treated for shock.
An unnamed 46-year-old man reportedly stole a knife inside the shop and “without warning, started hitting random people”, injuring five persons and killing one. He has since been arrested by police and taken into custody.