Gradkowski suffered a torn hamstring during the Steelers' opening preseason game last Friday, ESPN.com reports.
Gradkowski missed all of last season due to shoulder and hand injuries, so his hamstring problem only adds to his health issues. With Landry Jones cemented as the Steelers' No. 2 quarterback, Pittsburgh is fine behind Ben Roethlisberger, but Gradkowski's injury may open up their third-string job.