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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 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 findings through the Concussion & CTE Foundation.
Kneeland’s family, including his girlfriend, Catalina Mancera, released a statement.
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Dallas Cowboys defensive end Marshawn Kneeland (94) walks off the field after the game against the New Orleans Saints at AT&T Stadium in Arlington, Texas on September 15, 2024. (Tim Heitman/Imagn Images)
“While this diagnosis does not change the tragedy of his passing, it does provide important context about some of the struggles he may have faced. We are sharing this information to help people understand what NFL and other high-contact sports athletes may 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, 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 Mr. Kneeland’s brain, because we have found this progressive brain disease in nearly half of the athletes we have studied who have died before the age of 30,” McKee said in a statement through the Concussion & CTE Foundation.
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Dallas Cowboys defensive end Marshawn Kneeland (94) and defensive end Sam Williams (54) celebrate after returning a blocked punt for a touchdown during the game between the Dallas Cowboys and the Arizona Cardinals at AT&T Stadium in Arlington, Texas on Nov. 3, 2025. (Jerome Miron/Imagn Images)
“Thanks to the generosity of our brain donor families, we now better understand the earliest stages of CTE, 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, executive director 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 with concussion protocols and better helmets, and yet he still developed CTE,” Nowinski said.
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Dallas Cowboys defensive tackle Osa Odighizuwa (97) takes the field with a flag in honor of the late Dallas Cowboys defensive end Marshawn Kneeland before the game against the New York Giants at MetLife Stadium in East Rutherford, New Jersey on January 4, 2026. (Vincent Carchietta-Imagn photos)
“We have no reason to believe that the current generation has 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 severity of head impacts at all levels of the game.”
Kneeland started 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 days after he recorded his first NFL touchdown in a game against the Arizona Cardinals by recovering a blocked punt in the end zone.
