Brett Favre built a mystique during his 20-year NFL career not only as one of the game’s most prolific passers, but also one of its most durable quarterbacks.

Favre, who started 321 straight games from 1992 through the end of his career in 2010, estimated he suffered “thousands” of concussions during that time. The longtime Packers quarterback, who also played with the Jets and Vikings, made that estimation in an appearance on “The Bubba Army” this week.

Favre previously believed he only had three concussions during his playing career — instances which fit outdated understanding of what constitutes a concussion.

“If you had asked me this 10 years ago, how many concussions I had, I would have said three,” Favre said. “The reason I would have said three, I thought concussions were where you get knocked out, where you black out, for a period of time you don’t know where you are, memory loss, dizzy. A boxer gets knocked and tries to get up, his legs are rubber. That’s a concussion.”

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He said his understanding and definition of what constituted a concussion changed in more recent years, however. Favre said he realized that any time his head hit the ground — resulting in seemingly innocuous flashing lights or ringing ears — he had a concussion.

“So, based on that, thousands,” Favre said. “Had to be, because every time my head hit the turf, there was ringing or stars going, flash bulbs, but I was still able to play.

“That’s what’s kind of frightening about the concussion thing. It’s the ones that seem minor that do the damage, because you’re able to keep going, and still today, there’s probably guys that have them, they’re ‘I’m not going out.’”

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One of the most notable examples of Favre suffering a concussion appeared on the final play of his final game in the league. Favre took a rough sack against the Bears on “Monday Night Football,” leaving him face down on the ground for several moments before exiting the game.

Favre’s playing career essentially ended that play, as he was inactive for the remainder of the Vikings’ season.