A deceased professional hockey player has been found to have had brain damage associated with repeated head trauma, connecting hockey for the first time to health risks linked to boxers and, most recently, football players.

Reggie Fleming, a defenseman and left wing known for fighting as much as scoring in a long career from 1959 to 1974, was found by Boston University researchers to have chronic traumatic encephalopathy, a neurodegenerative disease known to cause cognitive decline, behavioral abnormalities and ultimately dementia. Fleming died in July at age 73 and was the first hockey player known to have been tested for the disease, known as C.T.E.

Fleming’s having had C.T.E. will stoke further debate in the National Hockey League this season over rules to decrease player concussions. Eleven former National Football League players have been found to have the same disease, catalyzing questions of football’s long-term health risks and miring the N.F.L. in three years of controversy over its handling of brain injuries.

“Boxing we’ve known for a long time, football we’ve recently become aware of  now hockey,” said Dr. Ann McKee, a neuropathologist at Boston University and the Bedford Veterans Administration Medical Center, who similarly diagnosed C.T.E. in several former N.F.L. players. “Repetitive head injuries can have very serious long-term consequences, regardless of how you get them.”