Murphy, a junior, sprained his shoulder against LSU on Oct. 12 and has been dealing with pain in every game since.
"He's sore. He's rehabbing," offensive coordinator Brent Pease said Tuesday. "He's in a situation where he's spending time in the training room getting healthy again. I think it's day to day based on what the trainers have to say.
"He's got to get in practice time at some point in time and be able to at least go out. … It's more his comfortability of how to throw, I guess. How well he can throw the ball with spin."
Murphy, who missed practice Monday and Tuesday, said he is especially frustrated at missing time after his four-turnover performance in a 34-17 loss to Vanderbilt last Saturday.
"It's very difficult just because after these last few losses and not playing well on Saturday, I need all the practice I can get," he said. "It's just frustrating being banged up a little bit and having to sit out and try to get healthy. I'm just gonna live in the training room and get healthy and try to get back out there as soon as possible.
"Going into the practices and stuff like that, I've been fighting a little bit of pain, but nothing too crazy. But when I get to the game, adrenaline takes over and I'm usually good to go."
When asked Monday if he could play if the game were today, Murphy said, "Most likely not."
Pease said Mornhinweg "is ready to go" and listed junior walk-on Christian Provancha as third on the depth chart.
"Skyler is a guy who's working very hard," Murphy said. "If his number's called, he's going to be ready to step up. I have a lot of confidence in him that if his number's called, he's going to be successful and do things to help his team win."
Despite never taking a snap in a college game, Mornhinweg appears to have the support of all of his teammates on offense.
"Skyler, he's been taking snaps at practice and just running with the ones and the twos to just get used to it and get a feel for it. So I'm pretty confident in him," fullback Hunter Joyer said. "He knows the playbook. If he has to get in there I think he'll do all right.
"He throws it pretty well. He's good at reading defenses and checking out of bad plays when we need him to. Just reading coverages and dumping it off, making smart decisions instead of always just trying to make a big play for us."