Pro Football Hall of Famer Brett Favre was known as the ultimate ironman in the NFL, having a streak of 297 consecutive starts over his career.

Now, Favre is warning parents about the dangers of playing football.

Favre, appearing in a new public service announcement, urges parents not to let children under 14 play tackle football, saying it would dramatically reduce the risk of being diagnosed with chronic traumatic encephalopathy, or CTE.

CTE currently can only be diagnosed post-mortem.

“Having kids play before high school is just not worth the risk,” Favre said in a statement. “CTE is a terrible disease, and we need to do everything we can to prevent it for the next generation of football players.”

Favre is partnering with the Concussion Legacy Foundation to “support athletes, veterans, and all affected by concussions and CTE; achieve smarter sports and safer athletes through education and innovation; and to end CTE through prevention and research.”