As a member of Serbian under-17 level, Radonjić scored 5 goals on 6 matches between 2012 and 2013, including a hat-trick in a match Belarus. Later, he had also been a member of the under-18 and under-19 national teams. Radonjić was called into the Serbia U20 national squad in November 2016 by coach Nenad Lalatović, when made his debut for the team in a match against Montenegro. As a coach of Serbia U21 selection, Nenad Lalatović also invited him to the squad for the 2017 UEFA European Under-21 Championship. In November 2017, Radonjić was invited to Serbia national football team for an Asia tour by caretaker Mladen Krstajić. He made his debut for Serbia in a friendly draw to South Korea on 14 November 2017, replacing Andrija Živković in 81 minute of the match.