The Ravens placed Mitchell (knee) on the PUP list Monday, Ryan Mink of the team's official site reports.
Mitchell, who is working his way back from a left ACL tear suffered last December, will unsurprisingly have to begin training camp on the PUP list. He can be moved to the active roster at any time during training camp and the preseason, once he's ready to practice, but if he remains sidelined by the time Week 1 rolls around, Mitchell will need to be moved to the reserve/PUP list and thus miss a minimum of four games to start the season. The undersized speedster is competing for a role behind Derrick Henry out of the backfield.