Like many other football professionals, Demaryius Thomas, who died in December at the age of just 33, suffered from chronic traumatic encephalopathy, or CTE for short.

This was the result of a brain examination by doctors from Boston University.

The former wide receiver, who won Super Bowl 50 with the Denver Broncos in 2016, was found dead in Roswell, Georgia.

The cause of death is not yet clear, according to Boston neuropathologist Ann McKee, Thomas most likely suffered a seizure.

CTE, a degenerative brain disease, "itself does not cause death," McKee clarified at ABC News: "CTE changes behavior and personality." According to family reports, Thomas was plagued by depression, anxiety attacks and panic attacks before his death.

NFL pros 'afraid to talk about it'

CTE occurs as a result of frequent head trauma and can only be detected postmortem.

The disease has already been detected in more than 300 former NFL players.

Among other things, Phillip Adams suffered from CTE, the former professional shot six people last year and then judged himself.

"I hope this is a wake-up call to current and former NFL players that CTE is prevalent among them and they need to get involved in developing real solutions," said Chris Nowinski, executive director of the Concussion Legacy Foundation (CLF), on the case Thomas.

The CLF is fighting for more awareness of the disease.

After Thomas' CTE disease became known, NFL professional Dez Bryant, among others, commented in this direction: "Many of us live with CTE and the NFL knows that," wrote the 33-year-old on Instagram.

But many of the athletes who have experienced these symptoms "are afraid to talk about it."