Roethlisberger likely suffered the injury in the AFC Championship Game on a hit by Ravens safety Haruki Nakamura.
Big Ben had this to say about the injury:
"Luckily, in the game, I didn't take any big hits to make 'em hurt. But I knew all along there was something wrong. There wouldn't have been anything they could have done about fractured ribs anyway. It was just suck it up and play.''
UPDATE: Turns out Big Ben could be making up another injury. ESPN reports that the Steelers had no knowledge of the alleged rib fractures. This could be another case of prima donna Big Ben trying to add to his own legend. Or it could be that the team is covering for Mike Tomlin's denial of Big Ben receiving x-rays before the Super Bowl.