Pecarski was a member of the Serbian under-19 team that finished 7th at the 2019 FIBA Under-19 Basketball World Cup in Heraklion, Greece. Over seven tournament games, he averaged 22.1 points and 8.6 rebounds per game. Pecarski was a member of the Serbian under-20 team that finished 15th at the 2019 FIBA U20 European Championship in Tel Aviv, Israel. Over six tournament games, he averaged 18.8 points and 8.8 rebounds per game.