Stanford quarterback K.J. Costello will not play in Saturday's Week 2 matchup with USC, head coach David Shaw announced Thursday.
Costello suffered a head injury in Week 1 after taking a forearm to the head. Davis Mills will start in his absence.
The Cardinal's rivalry tilt with the Trojans will now feature both backup quarterbacks, as J.T. Daniels was ruled out for the year with a torn ACL and meniscus.
Mills completed 7 of 14 passes for 81 yards after taking over for Costello last week against Northwestern.
