The Vikings signed safeties Shaun Prater and Anthony Harris to the 53-man roster Tuesday and placed safety Antone Exum Jr. on injured reserve.
The moves come less than 24 hours after all four safeties — Harrison Smith (knee/hamstring), Andrew Sendejo (knee), Robert Blanton (knee) and Exum (ribs/shoulder) — missed practice Monday.
Exum fractured a rib and injured the AC joint in a shoulder during Sunday's 38-7 loss to Seattle and will miss the rest of the season. Sendejo returned to practice Tuesday, but Smith and Blanton still were sidelined a day before leaving for Arizona for Thursday night's game against the Cardinals.
Prater was one of the final roster cuts after spending time with the Vikings in 2013 and 2014. He signed with Indianapolis but was waived in late October after playing in only one game. He has experience playing both cornerback and safety and on special teams.
Harris was promoted from the practice squad after joining the Vikings this spring as a rookie free agent out of Virginia. He also was one of the final roster cuts this summer but earned a spot on the practice squad.
"It's an opportunity to get on the field and go out there and do what I've been practicing and get better each week," Harris said. "I've been trying to focus up until this point, learn as much as I can just to be prepared for any situation that comes up."
Harris could be called upon to play a regular role with Smith and Blanton still sidelined. Nose tackle Linval Joseph (foot), linebackers Anthony Barr (groin/hand) and Brandon Watts (ribs) also missed practice for the second consecutive day.
To make roster room, the Vikings waived defensive end Justin Trattou.