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Former Dallas Cowboys defensive end Marshawn Kneeland, who died by suicide in November 2025 after a high-speed chase with police, was diagnosed with Stage 1 of chronic traumatic encephalopathy (CTE) in a postmortem brain tissue analysis.
There are four stages of CTE, with Stage 4 showing the most damage. The Boston University CTE Center diagnosed Kneeland’s brain, and his family released the results through the Concussion & CTE Foundation.
Kneeland’s family, including his girlfriend, Catalina Mancera, released a statement.
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“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. We share this information to help people understand what NFL and other high contact sport athletes might be struggling with,” the family said in a statement through the Concussion & CTE Foundation.
“Raising awareness is important to us. We continue to remember Marshawn with compassion for the person he was, rather than defining him by the final moments of his life. One Love.”
Dr. Ann McKee, the director of the Boston University CTE Center and chief of neuropathology for the VA Boston Healthcare System, said she was not surprised to find CTE in Kneeland’s brain.
“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,” McKee said in a statement through the Concussion & CTE Foundation.
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“Thanks to the generosity of our brain donor families, we now better understand the earliest stages of CTE, and it is bringing us closer than ever to diagnosing it during life. My team and I are fully dedicated to finding effective treatments and a cure for CTE.”
Dr. Chris Nowinski, the CEO of the Concussion & CTE Foundation, noted that Kneeland still had CTE despite playing in an era with concussion protocols and better helmets.
“Mr. Kneeland played in the modern era of concussion protocols and better helmets, and yet he still developed CTE,” Nowinski said.
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“We have no reason to believe the current generation is at a lower risk of CTE than previous generations. Concussion protocols do not prevent CTE, because CTE is caused by repeated head impacts, not just concussions. If we want to reduce CTE risk, we must implement CTE prevention protocols and aggressively reduce the number and strength of head impacts at every level of the game.”
Kneeland began playing tackle football when he was 7-years-old. He played at Western Michigan University before being selected in the second round of the 2024 NFL Draft by the Cowboys.
In 18 career games with the Cowboys, Kneeland recorded 26 tackles and one sack. His death came just days after he recorded his first NFL touchdown in a game against the Arizona Cardinals by recovering a blocked punt in the end zone.
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