The attacker killed the 30-year-old cashier after grabbing the weapons from the supermarket shelves, according to local media report.
A 46-year-old suspect was arrested by the police. The victims of the stabbing include the Arsenal centre-back who has been loaned out to Italian first-division league team Monza.
Arsenal Football Club (AFC), which plays in the first division of English league football released a statement on Mari's condition, saying that he is "recovering in the hospital and is not seriously hurt."