Head coach Jeff Fisher said Friday that Keenum will get the start but Goff will play as much as a full half against the Cowboys.
At least for one week, the 28-year-old Keenum has held off Goff in practice.
"I'm not looking as far forward as that," Keenum said Friday. "As far as that determining my confidence level, I don't think it will. I've got a job to do, and that's to lead the offense when I'm out there."
Goff, 21, was selected by the Rams as the No. 1 overall pick in the 2016 NFL Draft with anticipation that he will earn the starting quarterback job and become the face of the franchise in its new location. He played collegiately at Cal.
Fisher said he had not determined how many series each quarterback would play next Saturday.
"At some point we'll discuss it next week," Fisher said Friday. "It's nothing unusual. You know what you want to do. You play your starting quarterback with your starters and then you start subbing and then Jared comes in. He will get to play, probably quite a bit. He will probably play a half, but we'll discuss that."
In preparation for the preseason opener, the Rams on Saturday night were making their first team appearance back in the Coliseum -- taking a break from their summer camp at UC Irvine -- to hold a special practice and mini-scrimmage.
"When it's all said and done, I want it to be a great experience for the fans, a great experience for our staff and organization, and most of all, a productive day for our players," Fisher said.