Gary Plummer, now 58, played 11 seasons in the NFL with the San Diego Chargers (1986-93) and San Francisco 49ers (1994-97). The former linebacker won a Super Bowl with the 49ers in 1995 and racked up 1,029 tackles in his NFL career.

At this point, we know it's pretty much inevitable that any professional football player—especially a linebacker—is going to suffer some concussions throughout his career. Plummer's estimate of how many he suffered, however, is troubling.

"If you're not getting at least 10 of those a game, as a middle linebacker in the NFL, that means you didn't play that day," Plummer said on the 49ers Insider podcast. "I played 250 games. So (with) at least 10 a game, that's 2,500 concussions."

It should be noted that Plummer was including Grade 1 concussions, a.k.a. mild concussions, in his estimate.

Plummer's wife became concerned about the effects of CTE after Hall of Fame linebacker Junior Seau committed suicide at age 43 in 2012.

"After Junior, my wife said, 'Dude, you got to do something; I don't want you to be the next Junior Seau,'" Plummer recalled. 

Plummer detailed his efforts to protect and restore his brain.

"I felt myself not only getting better at the time I was doing those things, but it then became the cumulative effect of, 'Hey, there've been a few days where I didn't have a headache,'" Plummer said. "Or, 'There've been a few days where I've been able to sleep through the night.' And those were momentous occasions for me. It's been amazing that I literally feel like a new man."

Concussions have been pinpointed as a major reason the NFL's viewership numbers have declined, but—though that is certainly part of it—the situation is much more complicated.