His first league appearance came on the 26 February 2011 in Dinamo"s game against Karlovac. On 17 July 2014, Šitum joined Italian Serie B club Spezia on loan after a two-and-a-half year loan spell with NK Lokomotiva. In May 2015 he received a call-up to the senior Croatia squad for the friendly against Gibraltar and for a Euro 2016 qualifier game against Italy.
Šitum"s senior career began when he was promoted from the Dinamo Academy to the first team in 2011, making his first-team debut in the same year in a 3-0 win over Czechoslovakian side Sigma Olomouc. On the 19 February 2011 he started and played 75 minutes in a friendly against NK Istra 1961, which Dinamo won 4-3 at the newly renovated Stadion Aldo Drosina in Pula. Šitum started the match and scored in the 12th minute, a goal which turned out to be the game winner. Šitum started on a high note in the 2011-2012 season, scoring the fourth goal in a 5-0 win against NK Karlovac, and then scoring twice in a 4-0 win against NK Osijek. He scored again in the next round, netting the only goal in a win against NK Lučko. Internationally, Šitum scored his first goals for the Croatia under 21 side, during qualification for the 2015 Union of European Football Associations European Under-21 Football Championship in the match against Liechtenstein where Šitum scored the first two goals in a 4-0 win.
