Rivera was trying to catch a deep pass up the seam from Matt McGloin on Sunday when Griffin came in and lowered his helmet on the hit. Rivera's helmet flew off after the contact and he did not hold onto the ball. Griffin was penalized on the play and Rivera stayed down for a few minutes before walking off under his own power. He was taken to the locker room and is being evaluated for a head injury.
Oakland took Rivera 184th overall on Saturday with a pick acquired earlier in the day from Houston. The Raiders traded the 176th pick they acquired from Arizona earlier this month for the pick for Rivera and a seventh-rounder. Rivera caught 36 passes for 562 yards and five touchdowns last season for the Volunteers.