The brain of Steve Montador, a former N.H.L. player who died in February at age 35, was found to have widespread chronic traumatic encephalopathy, or C.T.E., a disease associated with repeated hits to the head.

His family plans to sue the N.H.L., lawyers representing Montador’s estate said.

Montador is the fifth former N.H.L. player known to have had C.T.E., which can be diagnosed only posthumously. Among its symptoms are memory loss, depression and problems with impulse control. Some with the disease show signs of progressive dementia.

Montador, a 10-year N.H.L. veteran known for his rough play and his willingness to fight, retired not long after sustaining a debilitating concussion in 2012 while with the Chicago Blackhawks. Montador, who also played for Calgary, Florida, Anaheim, Boston and Buffalo, was found dead in his home in Ontario in February. His cause of death has not been made public.

“Our thoughts, condolences and prayers remain with Steve’s family and friends,” the N.H.L. said in a statement Tuesday. “However, we do not agree that the reports and allegations made today establish any link between Steve’s death and his N.H.L. career.”