AC Milan midfielder Riccardo Montolivo is facing a lengthy period on the sidelines after suffering an anterior cruciate ligament (ACL) injury while on international duty.

Montolivo, 31, was substituted in the first half of Italy's 1-1 draw with Spain on Thursday.

On Friday, Milan confirmed on their official website that the playmaker injured his left knee and will now require surgery.

Montolivo signed for Milan from Fiorentina in 2012 and has since made 109 Serie A appearances.