I am looking for a story that was published in OMNI magazine in the 1970s or early 1980s. The protagonist is a fighter in an extremely bloody and violent sport. He has many body modifications to make him a more dangerous fighter. His opponents have arranged (out-of-ring) accidents for him that have left him scarred and mutilated, and a teleporter accident for his sister that has left her deformed.
He is facing his final match, and has bet on himself to lose. The opponent in the ring has been modified to look exactly like his sister, or possibly is his sister, kidnapped by the opponents' organization. In the end of the match he kills the opponent with a head blow, committing a double foul and thus losing.
The story was accompanied by an illustration of the very ugly protagonist.
I tried going through old OMNI magazines, but there are many and it is a long slog.