"I'm scared to death," Harrison said in an interview with NBC's
Harrison estimates that he suffered at least 20 concussions during his 15-year
Harrison said that the league didn't do enough to keep players safe during his playing days.
"I would get up, hit someone, the entire stadium is spinning around, and I would walk to the sideline and they would hold me out for one play, they'd give me two Advils, and they'd tell me, 'Get back into the game.'
"The NFL, if they're guilty of anything it's the lack of awareness that they brought and the lack of education that they told us.
"They never told us or explained to us or even let us know what a concussion was. I had no idea until just recently. And even since I retired from the Patriots in 2008, I would still experience headaches."
Harrison is speaking out following the recent suicides of former players