On 10 July 2019, Celar joined Serie B club Cittadella on loan until January 2020.[3] On 30 January 2020, he moved on loan to Cremonese.[4] After scoring two goals in eleven appearances during the 2019–20 Serie B season, his loan was extended for another season in August 2020.[5][6]
In the summer of 2021, Celar joined Swiss Super League club Lugano on a contract until 2025, joining his countryman Sandi Lovrić. He was given the number 19 jersey.[7] In his first season with the club, Celar won the 2021–22 Swiss Cup, and also scored in the final against St. Gallen as Lugano won 4–1.[8] Overall, he scored 40 goals in 95 appearances in the Swiss Super League over the course of three seasons, and was also the league's top scorer in the 2023–24 season.[9]
Between 2014 and 2021, Celar played for all Slovenian youth teams from under-16 to under-21, making 46 appearances for all teams combined and scoring 17 goals.[12]