As noted, WWE did the injury angle with Team Hell No at Extreme Rules because Kane had a legitimate injury to his left foot. WWE later announced that Kane suffered a broken ankle in the attack from the SmackDown Tag Team Champions.
PWInsider reports that he actually suffered an Achille’s tendon injury on the go-home show of Smackdown Live.
There’s no telling on when Kane suffered the injury as it could been in his brawl against The Bludgeon Brothers and SAnity or in the 10 man tag team main event.
Kane is not expected to be back on WWE TV anytime soon as he's preparing for the final push of his campaign to become the Mayor of Knox County, Tennessee this fall.