Three days before Stanford hosts UCLA, Cardinal coach David Shaw isn’t sure who his starting quarterback will be. The only thing certain is that it won’t be K.J. Costello.

Costello continues to be sidelined by a thumb injury and will miss his third consecutive game and fourth overall. He has made minor progress since being hurt but not enough to be cleared to practice.

Davis Mills, who passed for 775 yards and five touchdowns in his first three career starts as Costello’s replacement, is nursing a calf injury that forced him out of Stanford’s 23-13 upset of then-No. 15 Washington on Oct. 5.

Both Costello and Mills were held out of Monday’s practice. Costello has been ruled out against UCLA and the prospect of Mills playing isn’t much brighter.

“Davis is wavering between doubtful and questionable,” Shaw said “We’ll see what Davis can do maybe on Wednesday, maybe get out and run a little bit. Otherwise, if Davis can’t go Jack (West) will go play.”

A sophomore from Alabama, West took all the QB reps in practice Monday after playing the final 10 minutes against the Huskies after Mills went out. West did not attempt a pass against Washington but was sacked, although his lack of throws was because Stanford was holding a lead and trying to run out the clock.

If West is pressed to play against the Bruins, he won’t be going in cold. Although third-string quarterbacks generally run the scout team offense during defense-oriented portions of practice and get few, if any, reps with the starting offense, West took a lot of reps as the primary backup in spring ball than he normally would because of the situation with Costello. He’s continued to get the additional reps the past few weeks, too.

“I had a great conversation with Jack at the end of training camp,” Shaw said. “I said, ‘I have no issues with you playing. If you play, I know that we can run anything in our book.’ It was a compliment to how hard he’s worked. If he goes out to play, we’ll be able to run the whole playbook.”

Stanford’s injuries aren’t limited to the quarterbacks. The Cardinal finished the game against Washington with three true freshmen on the offensive line, which has been ravaged.

Shaw had hoped the 11-day break between games would give injured players time to heal. While it worked out that way for some, it didn’t for others.

In a strange way, the injuries have helped bring Stanford’s players closer.

“It hasn’t helped us but it’s rallied us,” running back Cameron Scarlett said. “Seeing a guy go down, you want to do all you can to make sure that you make a play for him. It’s definitely rallied us. We knew adversity was going to strike at some point in the season. Didn’t think that it would strike this hard, this fast, but we just have to respond to it and keep moving.”

Scarlett is a big reason why the Cardinal have overcome some of the injury issues. He ran for 97 yards in a loss to Oregon, followed it up with 92 when Stanford beat Oregon State, then piled up a career-best 157 yards on 33 carries in the win over Washington.

“We’ve put the ball in his hands and he’s done a great job of being physical and getting positive yards,” Shaw said. “Being able to run the ball and be balanced is a huge part of who we want to be.”

Michael Wagaman is a freelance writer.