Momirov was a member of the Serbian U-18 national basketball team that won the gold medal at the 2017 FIBA Europe Under-18 Championship. Over seven tournament games, he averaged 7.1 points, 3.1 rebounds, and 2.6 assists per game. He also participated at the 2016 FIBA Europe Under-18 Championship. Momirov was a member of the Serbian under-20 team that finished 15th at the 2019 FIBA U20 European Championship in Tel Aviv, Israel. Over seven tournament games, he averaged 8.4 points, 7.9 rebounds, and 3.6 assists per game.