(Reuters) - NFL linebacker Junior Seau, who committed suicide last year, had a debilitating brain disease, likely from 20 years of hits to the head, ABC News and ESPN reported on Thursday, citing researchers and his family as sources.

Seau, 43, died in May after shooting himself in the chest. He had played for the San Diego Chargers and had a 20-year career in the National Football League.

A study of Seau's brain by a team of independent researchers found that he had suffered from chronic traumatic encephalopathy, or CTE, the report said. CTE can only be diagnosed after death.

Tissue from his brain was sent to the National Institutes of Health for analysis in July at the request of Seau's family amid growing concerns over the long-term effects of football-related head injuries.

The NIH was not immediately available for comment.

(Reporting by Caroline Humer; Editing by Vicki Allen)