[Black Cats](http://www.thenorthernecho.co.uk/sport/football/sunderland) officials were unable to secure Aleksic a loan exit from Wearside before the English transfer window closed on Monday evening.
However, Polish clubs can still complete deals before September 8, and Aleksic has joined Cracovia, who currently sit second in the Polish top-flight after picking up 14 points from their opening seven games.
"At 20 years of age, Milan is a player who possesses the potential to progress to the next level, but to do this, he needs regular games in an appropriate environment," said Sunderland sporting director Kristjaan Speakman.
"Cracovia have made a positive start to the season domestically, and this move will provide Milan with the platform he needs at this moment in time. We wish him and Cracovia well as they challenge for the Polish title."
Aleksic joined Sunderland last summer from Serbian side FK Radnicki, but has struggled to make much of an impact during his time with the Black Cats.
He made his senior Sunderland debut as a substitute in last November’s 1-1 draw with Millwall, but only managed three starts and four more substitute appearances over the remainder of the Championship campaign. His only senior goal for Sunderland came in January’s FA Cup third-round defeat to Stoke City.
His only appearance in the current campaign came in the Carabao Cup second-round defeat to Huddersfield Town, when he left the bench to replace Wilson Isidor. It proved to be a notable one, however, as his missed penalty proved crucial as Sunderland exited the competition in a shootout.
A Serbia Under-21 international, the 20-year-old has featured in senior squads with his nation, but Regis Le Bris has clearly concluded he does not see Aleksic playing any kind of a role in the Premier League this season.
Aleksic is the second Sunderland player to move to Poland since the English transfer window closed, with Nazariy Rusyn having completed a season-long loan move to Arka Gdynia earlier this week.