The Steelers lost safety Shamarko Thomas during the team's 17-9 win over the Jacksonville Jaguars in Week 5 when he suffered a hamstring injury on special teams.
Thomas hasn't played on defense yet this season and has been only contributing on kick coverage. He's been effective in that role, and is considered the Steelers' top backup at strong safety behind Troy Polamalu.
Steelers coach Mike Tomlin addressed the injury after the game, but no timetable is available for his return, nor was any comment on the severity of the injury given. It wouldn't be usual for Thomas to miss extensive time, but hamstring injuries are difficult to heal quickly, so it may be an issue as the Steelers face the Cleveland Browns on the road in Week 6.
The Steelers traded up in the 2013 NFL Draft to acquire Thomas, a hard-hitting and athletic safety from Syracuse. That transaction was made with the Cleveland Browns, who would use the 2014 third-round pick they received in return to trade up with Philadelphia for the rights to take Johnny Manziel in the first round.