Junior quarterback Davis Mills will make his first career start for Stanford on Saturday instead.
Stanford quarterback K.J. Costello has been ruled out for the Cardinal's showdown against USC on Saturday, head coach David Shaw announced Thursday evening. Junior QB Davis Mills is expected to make his first career start for Stanford after replacing Costello in Week 1.
Costello had been listed as questionable earlier this week after exiting the Cardinal's season-opening matchup with Northwestern on Aug. 31 following a hit to the head late in the second quarter. The senior was 16-for-20 for 152 yards in his 25th career start before leaving the contest.
Stanford will also miss offensive tackle Walker Little on Saturday. Little is expected to miss "at least six weeks or so," per Fox Sports' Bruce Feldman. Little was named to Sports Illustrated's preseason All-America team on Aug. 16.
Stanford defeated Northwestern 17–7 on Saturday. The Cardinal are seeking their ninth straight winning season with head coach David Shaw in 2019.