"Eisbären Berlin is in shock", writes his club on its website.
The 26-year-old Eder played the World Championship as recently as May last year when Germany faced Sweden, among others.
In August, when this season was about to start, a malignant tumor was discovered during a medical examination of the players, writes German Sky Sport.
"Our deepest condolences go to his family, his fiancée, his friends and all who knew and loved him", writes the club.
Eisbären Berlin has become German champions three times in the last four seasons and Eder became a champion last year.
