The Panthers placed Roberts (knee) on injured reserve Tuesday, Darin Gantt of the team's official site reports.
Roberts, who dealt with a knee injury during the preseason, was diagnosed with a PCL sprain after playing in Sunday's season-opening loss to the Browns, per Tom Pelissero of NFL Network. Though Roberts will avoid surgery, he'll be forced to miss at least four games after landing on IR. In his absence, Shi Smith is expected to take over as the primary punt returner, while Chuba Hubbard and Laviska Shenault would be options on kickoffs.