UPDATE: Byron Leftwich has a second-degree sprain

Pittsburgh Steelers quarterback Byron Leftwich has a second-degree sprain of the medial collateral ligament in his left knee.

Leftwich, who was injured in Thursday night's preseason game, avoided a complete tear of the MCL, but nevertheless it remains a debilitating injury that is likely to prevent him from starting Pittsburgh's regular-season opener.

An MRI exam confirmed the injury, the sources said. Leftwich was expected to start during Ben Roethlisberger's suspension, which was reduced from six to four games, it was announced Friday.