"Reconstructive surgery"
His story is that his face got *beep* up because after the boxing he went to the wrong guy for his reconstructive surgery. But but... his last fight was in 1994. And after that he was most famously seen in Double Team (1997). Still looks like himself, just a bit older:https://image.tmdb.org/t/p/w300/beQ5z53Ym3AzgVd1tq7EhWzYTue.jpg
And then in 2001 in The Pledge, still looks like himself, well aged:
https://www.youtube.com/watch?v=Y4zHkIOsu0g
So I call *beep* on that story. He went under the knife out of vanity or whatever the *beep* ever, but no way did his boxing injuries made him do it.