Blake Bortles could miss as much as a week of practice while he heals from a minor hand injury.
The junior quarterback, who was spotted at Thursday's media day wearing a soft cast on his right throwing hand, suffered a "thumb contusion" during the Knights' second practice earlier that day.
He worked on some footwork drills at Friday's workout, but stood on the sidelines as the backups received all the reps at quarterback.
UCF coach George O'Leary said Bortles could continue practicing, but he always exercises caution in these situations.
"He can go, but my experience with those things is to let them heal," O'Leary said. "I pushed a kid back once and all of a sudden it was the whole season with him because he aggravated it. I want to make sure the swelling goes down.
"He hit someone's helmet. Typical. I sent him to the doctor this morning. He has a thumb contusion. That's what he has. I may not play him for a week to make sure that's fully healed which is the smart thing to do. He understands. I'm more worried about cardiovascular (conditioning) and all that. We'll be fine. Plus it gives me a chance to evaluate those other quarterbacks."
Junior Tyler Gabbert enters the preseason as Bortles' backup. Splitting time on the third team have been a pair of true freshmen, Pete DiNovo and Justin Holman, both of whom enrolled earlier this spring.
Light hitting took place on Friday as UCF put on shoulder pads for the first time. Sunday will be their first full gear, full contact practice.
"I thought the individuals were real good," O'Leary said. "I thought team got sloppy at the end. Gun snaps were sloppy. I think basically the defense is always ahead of passing as far as the offense is concerned. Obviously there are people to throw it to. I like what we're doing in the run game. We'll just get better and better as we work."
UCF looks to have a solid one-two running back tandem in Storm Johnson and Cedric Thompson. There's room for another in the rotation and it could go to one of the three players in the freshman class, which include Micah Reed, Will Stanback and Dontravious Wilson.
Stanback, who is a solidly-built 5-foot-11 and 205 pounds, has already impressed O'Leary.
"The kid that keeps catching my eye is Stanback," O'Leary said. "I think we've got some really good freshman running backs in the program. Hopefully they can keep developing and developing and I think we'll be better if that can be done."
Stanback wears No. 28, the same number that belonged to All-Conference running back Latavius Murray, now in his rookie training camp with the Oakland Raiders. Like Murray, Stanback is also a New York native.