It's a condition linked to athletes who have experienced repeated concussions.
The Chicago Tribune reports that Duerson died of a self-inflicted gunshot to the chest and that his death has been ruled a suicide.
A representative from a center that studies degenerative brain conditions at Boston University School of Medicine says he was contacted by the NFL Players Association and he also spoke with a representative of Duerson's family.
Duerson died in Florida on Thursday.
He was a member of the 1985 Super Bowl Bears.