In 2014, Đerlek was invited into Serbian under-15 national team under coach Marko Mitrović. He scored a goal in a debut match for the team against Montenegro on 9 December 2014. He also scored against the Netherlands on 11 February 2015. Đerlek continued playing with Serbian under-16 selection between 2015 and 2016, scoring in matches against Poland and Macedonia, and in a match against Montenegro on 10 June 2016, when he scored a hat trick. He also scored on his debut match for Serbian under-17 level against Hungary on 8 December 2015. He played performed as a captain until summer 2017, helping the team to qualify on the UEFA European Under-17 Championship in 2016 and 2017. In December 2017, Perica Ognjenović called Đerlek in Serbian under-18 national team for the tournament in Israel. He made his debut for the team as a captain in 1–0 defeat against home team on 11 December same year, and also played against Germany next day.