Before he shot himself fatally in the chest Thursday, the former Chicago Bears defensive back Dave Duerson sent family members text messages requesting that his brain tissue be examined for the same damage recently found in other retired players, two people aware of the messages said Saturday night.

As a longtime force in the N.F.L. players union, Duerson, 50, was keenly aware of chronic traumatic encephalopathy, the degenerative brain disease linked to depression, dementia and occasionally suicide among more than a dozen deceased players. He had expressed concern in recent months that he might have had the condition, said one person close to him who spoke on condition of anonymity.

The Duerson family got in touch with representatives of Boston University’s Center for the Study of Traumatic Encephalopathy, said Dr. Robert Stern, a co-director of the research group. Stern declined to comment further on Duerson’s specific case because of policies about confidentiality.

“This is a tragic event,” Stern said. “His wish will hopefully lead to additional scientific answers about this disease.”