According Entertainment Weekly, Visnjic will play a Yugoslavian immigrant on four episodes of the 1960s-set drama.
The character is said to be torn between his communist homeland and the opportunities presented by life outside the Eastern Bloc.
After leaving 'ER,' Visnjic did a guest spot on 'Leverage' and appeared in the BBC minseries 'The Deep.'
'Pan Am' stars Christina Ricci and Mike Vogel and follows the exciting lives of Pan Am flight attendants and pilots. The series takes place during the height of Pan Am's high-flying jet-setting days.
Catch a preview of the new series after the jump.
'Pan Am' premieres Sun., Sept. 25 at 10PM ET on ABC.