A source confirmed that Richardson sustained a neck injury similar to the one he had in 2012.
The backup defensive back and special teams standout was added to the injury report on Thursday, and the Milwaukee Journal Sentinel first reported Friday the severity of the injury.
Although it was not clear when Richardson was injured, it's the second time in his career that he sustained a neck injury. In 2012, Richardson sustained a herniated disk that required neck fusion surgery. Because the fusion was lower in his neck than other players who couldn't come back from similar injuries, the Packers medical staff cleared him to return late in 2013.
Richardson was one of the few recent Packers players to return from neck fusion surgery. Safety Nick Collins and tight end Jermichael Finley were never cleared by the team to return and have not played in the NFL since their injuries.
The fourth-year pro played in every game last season, mostly on special teams, and was retained when the Packers matched a one-year, $2.55 million restricted free agent offer sheet he signed with the Oakland Raiders this offseason.
The Packers did not immediately place Richardson on injured reserve, but they might be short-handed at safety for Sunday's game against the Rams if they don't make a roster move. With Morgan Burnett (calf) listed as questionable, the Packers currently have only three healthy safeties on the roster: Ha Ha Clinton-Dix, Micah Hyde and Chris Banjo.