Here is the entire inactive lists for both teams:
Jennings had practiced all week, passing the first phases of the concussion protocol. He traveled with the team but apparently in the end was unable to pass the final tests to be cleared to play.
With Jennings out, the running ball duties fall to Marcel Reece and recently converted, Taiwan Jones. Reece is the team's fullback and Jones as recently as last week was still listed as a cornerback for the team. He switches back to the position he played for his first two years with the Raiders.
This isn't the best time to have this happen as the Raiders are going against the number one run defense in the NFL which means if the Raiders are to move down field, it could bee on the arm of Matt McGloin.