Italy's Carabinieri police said one person had died in Thursday's attack, a 47-year-old Bolivian national who worked at the supermarket in the town of Assago. Another employee was injured along with four customers, including Mari.

A 46-year-old suspect was detained but the motive was not clear, the Carabinieri said.

They said late on Thursday the suspect had mental health disorders and was under guard in a psychiatric ward.

Milan's Niguarda hospital said on Friday Mari was in a stable condition, having suffered non-deep stab wounds in his back. It said in a statement he had arrived at the hospital "alert and conscious" and was due to have an operation to suture the wounds.

A spokesman for his Serie A side confirmed he was due to have surgery but said he had no further details.

Monza Chief Executive Adriano Galliani had said on Thursday Mari's life was not in danger and he should recover quickly, calling him a "warrior".

Galliani also said on Twitter: "Dear Pablo, we are all here close to you and your family, we love you, keep fighting as you know how to do, you are a warrior and you will get well soon."

He also clarified his condition: “Pablo Mari had a fairly deep wound on his back, which fortunately did not touch his vital organs such as the lungs or others. His life is not in danger, he should recover quickly," 

Mari, has been an Arsenal player for three-and-a half seasons and played under Mikel Arteta. The Gunners manager also said that the club had been in contact with Mari's relatives.

"I just found out. I know (technical director) Edu has been in touch with his relatives. He's in hospital but he seems to be okay."

Arteta was speaking at a news conference after his team's match away to PSV Eindhoven in the Europa League.