Former Dallas Cowboys defensive end Marshawn Kneeland, who died by suicide in November 2025, has been diagnosed with chronic traumatic encephalopathy (CTE), Boston University doctors announced Tuesday.
The 24-year-old's brain was examined posthumously at the BU CTE Center, revealing Stage 1 CTE — the earliest stage of the disease, associated with short-term memory loss, mild aggression, depression, and headaches.
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“Unfortunately, I was not surprised to find CTE in the brain of Mr. Kneeland, because we have found this progressive brain disease in nearly half of the athletes we’ve studied who have died before the age of 30,” said Dr. Ann McKee, director of the BU CTE Center.
Kneeland played only 18 NFL games over two seasons but had played tackle football since age seven.
“While this diagnosis does not change the tragedy of his passing, it provides important context about some of the struggles he may have been facing,” said Catalina Mancera, Kneeland's girlfriend.
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Chris Nowinski, CEO of the Concussion & CTE Foundation, noted that Kneeland played in the modern era of concussion protocols and better helmets yet still developed CTE.
“We have no reason to believe the current generation is at a lower risk of CTE than previous generations.
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Concussion protocols do not prevent CTE, because CTE is caused by repeated head impacts, not just concussions,” he said.
Kneeland was mourned by family, friends, fans, and teammates, with Cowboys head coach Brian Schottenheimer fighting back tears, calling him a “beloved teammate.”
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