Prater, 23, was released by the Philadelphia Eagles on Monday, having appeared in one game this season. He played on special teams and didn't record any statistics. Minnesota released cornerback Jacob Lacey, who was re-signed last week, to make room for Prater.
Prater, 5-foot-10 and 190 pounds, was a fifth-round draft pick by the Cincinnati Bengals in 2012 out of Iowa.
A day after Monday night's 23-7 loss at New York, Vikings coach Leslie Frazier didn't have much more of an update on the team's injury situation. Running back Matt Asiata (shoulder) and tight end Rhett Ellison (ankle) weren't able to finish Monday's game. Both are expected to have magnetic resonance imaging tests this week.
Frazier said running back Adrian Peterson (hamstring) and left tackle Matt Kalil (back) didn't have any issues playing Monday with their injuries.
Frazier said any limitation on Peterson "didn't come up" and he was pleased to see Kalil be able to finish the game after not practicing on Friday and Saturday.
"He did pretty good, it was great to see him finish the game," Frazier said of Kalil. "He played fairly well, obviously could have done some things better, but he finished the game which is great, because we were really concerned prior to the game whether he'd make it."