SANTA CLARA -- For the first time in his career, Dallas Cowboys left tackle Tyron Smith has missed two games in the same season.

Smith missed Sunday’s win against the San Francisco 49ers because of a back issue that popped up two days before the Cowboys beat the Chicago Bears on Sept. 25.

He is working through a bulging disc in his back that owner and general manager Jerry Jones said is not uncommon for players on the team, however, a source said the disc is symptomatic at the moment.

"Tyron has something that probably a huge percent of this league has," Jones said. "It is not something that we would directly list on our report, and so it’s very common. It’s very common. It’s very common. And it’s more now like a muscle spasm. I would couch it as a muscle spasm. Treatment is more like that than it is anything to do with what I would consider traditional looks at bulging discs and things like that."

Jones said "it wouldn’t surprise me at all," if Smith plays this week against the Cincinnati Bengals. Last Thursday, Smith said he was feeling much better, but he did not practice during the course of the week.

Before the 49ers' game, Smith worked through resistance training, which is what he did last week instead of practice.

Chaz Green has started the past two games at left tackle. After drawing three penalties against the Bears, Green was penalty-free against San Francisco.

"I’m just trying to do my part," Green said. "I don’t want there to be a drop-off when I get in there. I just want to step up and help the team out the best that I can."