McMahon joins former Bears teammate Steve McMichael, who is head coach of the Slaughter.
And the son of Bears Hall of Fame running back Walter Payton has signed on to play this season. Like his late father, Jarrett Payton will play at running back.
McMahon, McMichael and Walter Payton were all on the 1985 Bears, the last Chicago team to win the Super Bowl.
The Slaughter's first game of the season is Feb. 27. The team went undefeated to win the Continental Indoor Football League Championship in 2009.