Report: Stanford QB K.J. Costello out Saturday against USC

John Hefti-USA TODAY Sports

Two of the best-known quarterbacks in the Pac-12 will not be on the field when Stanford and USC do battle Saturday in Southern California.

Trojans sophomore quarterback J.T. Daniels is out for the season with a torn ACL. Meanwhile, Cardinal quarterback K.J. Costello has been ruled out with a head injury he suffered in Stanford’s season opener last week against Northwestern.

This is a major blow for David Shaw and the 23rd-ranked Cardinal. The senior entered this season as an under-the-radar pro prospect and was being relied on to help a rather youthful Stanford offense.

With Costello out of action, junior Davis Mills will make his first career start. He completed 7-of-14 passes last week and has 16 career pass attempts to his name.