Jefferson left Monday's practice due to a leg injury, Kyle Meinke of MLive.com reports.
Jefferson had a strong start to camp and was expected to have a large role in Friday's preseason opener against the Bills as he competes for the No. 3 running back role ahead of Week 1. The severity of the rookie's injury isn't yet known, but Dedrick Mills, Michael Warren and Godwin Igwebuike could see increased work if Jefferson is limited or held out Friday.