Marko, 24, joined City in July 2012 following a spell in the Championship with Portsmouth and made 12 appearances during his debut season - scoring in a Capital One Cup defeat to Burton Albion and in a memorable 6-0 win over Ipswich Town.
He spent time on loan with Blackpool towards the end of that season, before spending most of last season on loan with Hungarian club Diósgyőri VTK.