He was still only 18 years old when he went on to make three appearances for Dinamo Zagreb in the UEFA Champions League group stage in the autumn of 1998, starting in two matches and becoming notable for scoring the club's first goal in the UEFA Champions League when he opened the scoring in the 7th minute of Dinamo's fourth group match, against Porto at home in Zagreb.

Dinamo won the match 3–1 and went on to win 1–0 against Ajax Amsterdam away and draw 1–1 against Olympiacos at home, but failed to advance to the quarterfinals after finishing second in their group.

He also played with Dinamo Zagreb in the UEFA Champions League in the following year and made five appearances in six group matches, but was a starting player only once.

He did not manage to score any goals in a total of 29 competitive appearances for Kaiserslautern and left the club in June 2006, shortly after they were relegated to the 2.

Mikić's domestic league debut for Rijeka came on 30 July 2006 in the club's opening match of the 2006–07 season, where they celebrated a 4–3 away victory against Cibalia.

He continued to play for the Croatian under-21 team until November 2001, making six appearances and scoring three goals in their qualifying campaign for the 2002 European Under-21 Championship.