The Chargers signed Johnson to a reserve/future contract Tuesday.
Johnson caught on with the Chargers' practice squad in late August after failing to make the Packers' 53-man roster at the end of training camp. He was elevated to the Chargers' active roster in Weeks 9 and 11 and logged two carries for eight yards while failing to haul in his lone target. The South Dakota State product will be a member of the Chargers' 90-man roster at the start of the NFL offseason Feb. 9, which will allow him to participate in OTAs and minicamp.