Born in Pula, SR Croatia, Yugoslavia, Aleksić was several months old when his mother fled to Serbia due to the ongoing Croatian War of Independence.

[3] During Vojvodina's 2008–09 season opening league match, a derby versus Red Star Belgrade, Aleksić scored a 90th-minute goal to put the game beyond reach and ensure a famous 2–0 win for his team.

[4] In November 2008, Aleksić started to figure as a transfer target for Serbia's biggest clubs – Red Star and Partizan – however, Vojvodina officials at the time were adamant that they would never sell him to league competitors.

[5] In late March 2009, he reportedly also started getting attention form abroad with scouts from Real Madrid and Villarreal coming to watch him play for the Serbian U19 national squad.

Playing under head coach Gian Piero Gasperini, Aleksić made his Serie A debut against Juventus on 14 February 2010, coming on as the 88th-minute substitute for Domenico Criscito, a game which Genoa lost 3–2.

Aleksić joined Lechia Gdańsk during the 2014 summer transfer window on a two-year contract,[13] making his debut in a 3–1 defeat to Wisła Kraków.

Aleksić led his team single-handedly all the way to the final group stage and was the main contender for the U17 golden boot award for most goals.

Aleksić made his senior national team debut as a 17-year-old in December 2008 under head coach Radomir Antić in a friendly versus Poland, making him one of the youngest debutantes ever.