[3] Vujačić made the Partizan debut on his 25th birthday, after he came on as a sub during the third round UEFA Europa League qualifier against Yeni Malatyaspor.

Just one month after the start of the new season, Aleksandar Stanojević became the new coach of Partizan and Igor slowly became a regular first team player.

[7] On 12 August 2021, Vujačić played a big role in a return match of the UEFA Europa Conference League Third qualifying round against Sochi when he kicked the ball off the goal line in the 103rd minute of extra time and later during the penalty shootout he scored a fourth penalty that took Partizan to Play-off round.

A great action by Partizan started by Bibras Natcho from the free kick, the ball came to Aleksandar Šćekić who headed it to the other side to Vujacić.

On 30 June 2023, Partizan announced that Vujačić left the club for the Russian Premier League side Rubin Kazan.