Pablo Mari, the Arsenal defender who is on loan at Monza, is in hospital after being stabbed at a shopping centre on the outskirts of Milan.
The 29-year-old was one of several people injured during an incident at a supermarket in Carrefour.
Monza confirmed Mari is receiving care at Niguarda hospital in Milan, but his condition remains unknown.
According to reports, the suspect was arrested by police and subsequently taken into custody.
Mari has made eight appearances for Monza in Serie A this season, scoring in their 2-0 victory over Spezia earlier this month.