Brett Favre was diagnosed with "three or four" concussions during his career, but the Hall of Fame quarterback guesses he had "probably thousands."
Favre, who has become an advocate for concussion research, worries about chronic traumatic encephalopathy (CTE) after taking the number of hits he took in a 20-year, 302-game NFL career.
"As we're learning about concussions, there's a term we use in football and maybe other sports, that I got 'dinged,'" Favre told NBC's Megyn Kelly Today, via The Associated Press. "When you have ringing of the ears, seeing stars, that is a concussion.
"If that's a concussion, then I've had hundreds, probably thousands, throughout my career, which is frightening."
Abby Wambach, David Ross and Kurt Warner joined Favre on Kelly's show. The four star athletes are investors in a company developing a concussion-treatment drug not yet approved by the Food and Drug Administration.
Favre, 48, said he would discourage boys from playing football with "no treatment solution out there."