After playing for Crvenka, Portner joined Yugoslav champions Metaloplastika, becoming a member of the squad that won consecutive European Cup titles (1984–85 and 1985–86).

[3][4] He reunited with his former Metaloplastika teammate Veselin Vujović, helping the club win the European Cup in 1991.

He later also played for Swiss teams BSV Bern, TV Zofingen, and BSC Grosshöchstetten.

[5] At international level, Portner represented Yugoslavia in two World Championships, winning the 1986 edition in his debut appearance.

[6] While playing in Switzerland, Portner started his coaching career with BSV Bern.