The 40-year-old injured his left cheekbone in a duel with Juventus' Manuel Locatelli during Sunday night's league match. Modric left the field with an ice pack pressed to his cheek.
According to a statement from Milan, Monday's examination showed surgery is necessary and will be performed immediately. Milan did not say how long Modric is expected to be out of football. Typically, a cheekbone fracture takes about a month to heal.
The match between Milan and Juventus ended 0–0.
