Marsh won't return to Sunday's game against the Saints and is being evaluated for a concussion, Craig Grialou of 98.7 FM Arizona reports.
It's unclear how Marsh picked up the injury, but he will enter the league's mandated concussion protocol. Marsh will need to gain clearance before returning to the field for next week, but now that he's officially out, Brooks Reed is the only healthy depth outside linebacker on the roster.