The New York Times says former NHL enforcer Derek Boogaard showed signs of a degenerative brain condition believed to be caused by repeated blows to the head.
Boogaard's family donated his brain to the Center for the Study of Traumatic Encephalopathy at Boston University's School of Medicine.
The 28-year-old former New York Rangers forward died in May due to an accidental mix of alcohol and the painkiller oxycodone.
The Times says research shows Boogaard had chronic traumatic encephalopathy, commonly known as C.T.E., a close relative of Alzheimer's disease.
The newspaper says scientists were shocked to see so much damage in someone so young. And that had Boogaard lived, his condition likely would have worsened into middle-age dementia.
Boogaard played parts of five seasons with the Minnesota Wild before signing with the Rangers as a free agent in the summer of 2010.
In 277 career NHL games, the six-foot-eight, 257-pound Saskatoon native recorded three goals, 13 assists and 589 penalty minutes.