Pittsburgh punter Cameron Johnston sustained a serious right knee injury in Sunday's 18-10 season-opening victory over the host Atlanta Falcons, Steelers coach Mike Tomlin said after the game. Johnston, who will have an MRI on Monday to determine the severity of his injury, was hurt with 3:40 left in the fourth quarter when he was run into by a Falcons defender. A holding penalty on Pittsburgh led to a new fourth down, with kicker Chris Boswell stepping in and booting a 43-yard punt. "Cam Johnston appears to have a serious injury. I'll have an update for you next time we come together," Tomlin said at a postgame press conference.