PITTSBURGH -- The Pittsburgh Steelers made several roster moves, highlighted by the signing of safety Trenton Thompson to the active roster while also placing defensive back Elijah Riley on Injured Reserve. 

Riley left Week 11 in the second half after suffering an ankle injury. Afterward, the was reported the defensive back was dealing with a high ankle issue, which will now force him onto IR for an unforeseen amount of time. 

The Steelers could open Riley's return window in four weeks, but the severity of the injury is unknown. Therefore, as of now, there is no known timetable for his return. 

To fill his spot, the Steelers will sign Thompson to their 53-man roster. Thompson was elevated from the practice squad the last two games in Minkah Fitzpatrick's absence. With Keanu Neal being placed on IR after a rib injury, Thompson stepped into the starting role alongside Damontae Kazee. 

He finished Week 11 with six tackles and two pass deflections and nearly picked off Dorian Thompson-Robinson while covering Amari Cooper. 

Until Fitzpatrick returns from a hamstring injury, expect Thompson to start for the Steelers at safety. With Neal and Riley on IR, he'll likely remain in the team's three safety sets once Fitzpatrick returns. 

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