Mariota, who was placed on injured reserve Monday, is dealing with a strained pectoral, Ian Rapoport of NFL Network reports.
After tending to shoulder and ankle injuries in the offseason, Mariota was hindered by an unknown issue for the later stages of training camp. The Raiders "hope" that the time away from the field helps him heal and eventually handle backup QB duties behind Derek Carr, but those will be covered by Nathan Peterman for at least the rest of September