Career
He used to represent Serbia at Under-19 and Under-20 level Čukarički
He scored his first competitive goal for the club in a 1–4 away loss against Red Star Belgrade on 12 April 2014. That was his only goal in four league appearances in the 2013-2014 season.
Mandić represented Serbia at the 2014 Union of European Football Associations Under-19 Championship.
He scored the winning goal in the 90th minute against Bulgaria, taking the team to the semi-finals of the tournament, as well as securing them a spot at the 2015 Fédération internationale de football association U-20 World Cup. After returning from the U20 World Cup in New Zealand, Serbia U21 coach Tomislav Sivić made his squad for the 2017 Union of European Football Associations Euro U21 qualifiers, which did not include Mandić.
Vladimir Matijašević, Čukarički"s sports director, wrote a letter to Sivić which garnered national publicity when he suggested that Sivić was selecting players for the U21 team based on their agents and not their qualities as players. On August 31, 2015, Mandić announced that he accepted an invitation from the Football Association of Montenegro to play for the Montenegrin national team