A former Super Bowl champ says his face was busted open BAD during an NFL game -- opening a gash that needed 17 stitches to close ... and he blames the whole thing on a shoddy helmet.
The guy behind the lawsuit is ex-Chicago Bears safety Ryan Mundy -- who says he was involved in a hit during a 2014 pre-season game against the Seahawks.
Mundy says as a result of the collision, the sharp plastic edge on the padding, lining the inside of his Schutt helmet, sliced into his forehead and opened up a 5 AND A HALF INCH GASH.
Mundy -- who was part of the Steelers' Super Bowl 43 squad -- says he got the wound stitched up ... but he now has permanent skin discoloration at the scar site.
To make matters worse, Mundy claims Schutt KNEW its helmets were ripping open other players before the incident -- but did nothing to remedy the problem.
Now, Mundy is suing Schutt -- and in the lawsuit, filed by attorney Richard Gordon, the 31-year-old claims he's suffered permanent pain, mental anguish, and lost capacity for the enjoyment of life.
We reached out to Schutt -- but a rep had no comment.