Gus Johnson feels the good, bad of Cowboys preseason

Undrafted rookie Gus Johnson holds on to the ball after scoring his first NFL touchdown. Orlando Jorge Ramirez/USA TODAY Sports

SAN DIEGO -- Gus Johnson's Thursday started incredibly well and ended incredibly poorly.

With Joseph Randle (oblique), Darren McFadden (hamstring) and Lance Dunbar (ankle) not playing in the Dallas Cowboys' preseason opener against the San Diego Chargers, Johnson started at tailback. He ended the night early with a third-quarter shoulder injury.

Johnson admitted disappointment with the injury.

"Just football, that's it," Johnson said. "You get bruises and stuff like that. It's fine."

Coach Jason Garrett said Johnson suffered an AC separation, which could lead to some time off. The Cowboys return to practice on Saturday and McFadden is expected to make his training camp debut. Dunbar has upped his rehab and could return in the next few days, and Randle could also be back to taking part in team drills shortly.

Johnson's moment might be brief, but at least he had one, which is not something a lot of undrafted free agents can say.

He finished with 35 yards on 13 carries and scored the Cowboys' only touchdown, a 5-yarder in the second quarter.

"It's one of those feelings you can't really describe," Johnson said of his score. "You just think about it and start smiling. It's one of those feelings."

Johnson had some help getting into the end zone from his offensive line with the hole and some pushing.

"Had to make a linebacker miss and then once contact was made I had all my buddies behind me helping me push forward," Johnson said. "I think that's what made it a great experience because I'm probably not getting in without them."

Johnson didn't spike the ball in celebration.

"I know I wasn't letting the ball go," Johnson said. "You got to keep the ball."

Members of the equipment crew kept it in a safe place.

If Johnson doesn't make the 53-man roster or practice squad, he will always have the ball from his first touchdown, even if it came in a preseason game.

"He was out there with the ones, our ones and their ones," coach Jason Garrett said. "That's a great opportunity for a young guy. I thought he handled himself well. He stuck it up in there a few times. He made some good runs for us. Overall, we didn't run the ball as well as we need to run and he was part of that. But everybody was a part of that."