[1] Next summer, he has joined the first team of Spartak Subotica,[3] but shortly after he returned to Bačka 1901, this time as a loaned player until the end of 2015–16 season.
[4] At the beginning of 2016, Ćalasan signed his first professional contract with Spartak Subotica,[5] and in summer of the same year, he became a regular member of the first squad.
[9] During the 2017–18 season, Ćalasan made 31 appearances in both domestic competitions under coaches Aleksandar Veselinović and Vladimir Gaćinović, finishing at the 4th place of the SuperLiga table.
[9] Ćalasan made his first continental appearance in the first leg of the First qualifying round for 2018–19 UEFA Europa League campaign, against Coleraine, pairing with Dejan Kerkez as a centre-back.
[12] Ćalasan was called in Serbia U20 national squad by coach Nenad Lalatović, and made his debut for the team in a match against Montenegro in November 2016.