[2] In September 2021, Kostadinov joined Levski Sofia as the first signing of new manager Stanimir Stoilov.
He was particularly prolific in the Bulgarian Cup competition scoring four goals in three games, thus helping his team reach the semi-finals of the tournament.
In March 2022, however, Kostadinov along with team-mate Zdravko Dimitrov were suspended from the first team due to disciplinary issues, later identified as gambling "addiction".
[5] On 1 February 2024, Kostadinov joined Crotone in Italian Serie C on loan with an option to buy.
[6] Kostadinov made his debut for the Bulgaria U19 team on 12 September 2017 in a match against Bosnia and Herzegovina U19.