The Raiders announced Pryor was being evaluated for a head injury:
QB @TerrellePryor has a head injury and is being evaluated.— OAKLAND RAIDERS (@RAIDERS) September 24, 2013
Afterward, it was announced Pryor suffered a concussion, as noted by Scott Bair of CSN Bay Area:
Official now. Terrelle has been formally diagnosed with a concussion. Tracy porter too. #raiders— Scott Bair (@BairCSN) September 24, 2013
Pryor was active for Week 5.