He also played for Deportivo de La Coruña, Bayern Munich (winning the UEFA Cup with them in 1996 and scoring in the final itself), Fenerbahçe, Mainz 05, and UANL Tigres.

Kostadinov gained international prominence after scoring two goals in the last matchday of the European 1994 World Cup qualification, against the France national team.

He scored his second goal in the last second of the match with a shot with his right foot from inside the French penalty area that sent the ball into the roof of the net.

After helping Bulgaria qualify for the 1994 World Cup, he was a part of the squad that reached the semi-finals in the proper tournament, again in partnership with Hristo Stoichkov.

During the game against Italy in the semi-final, Kostadinov was fouled by Alessandro Costacurta in the penalty area, who later committed a handball offence there as well.