Gradkowski, who is entering his 10th NFL season, suffered the injury in the preseason opener against the Detroit Lions.
Steelers coach Mike Tomlin said Monday that Gradkowski's hamstring injury involves "soft tissue" and Gradkowski will "be out a number of weeks."
The Steelers could place Gradkowski, 33, on injured reserve for the second straight year or wait out the injury. Gradkowski missed all of 2015 with shoulder and hand/finger injuries. This offseason, he re-signed with the team on a one-year deal.
Landry Jones has solidified the No. 2 quarterback job behind Ben Roethlisberger, but behind him is project Dustin Vaughan, who has never taken an NFL snap and was cut in Dallas Cowboys camp last year.
For his career, Gradkowski is 375-of-709 for 4,057 yards, 21 touchdowns and 24 interceptions.