Peters suffered back spasms in the Eagles' 27-16 loss to the Carolina Panthers on Oct. 25. Even though the team had its bye last week, Peters only practiced once this week, an abbreviated workout Tuesday.
Johnson, who practiced all week on the left side, would likely see a lot of matchups against Greg Hardy, who has three sacks in three games for the Cowboys since returning from a four-game suspension.
''He's a guy who never stops. He comes at you really hard and he's a guy who gives a lot of effort,'' Johnson said. ''The challenge for me is not having a lot of time to get ready for it. One week isn't a lot of time. I'm going to go out there, give it my best and I think I'll do well.''
Kelly, a fifth-round draft pick out of Purdue in 2012, has dressed for five of the Eagles' seven games this season and is a backup at both guard and tackle.
In his four-year career he has started 13 games, seven at right tackle.
''We're getting there,'' Kelly said. ''It's not going to be a perfect fit right away. We've had a really good week of training so far. So we'll see how it goes. We'll be ready.''
The Eagles are hoping Ryans will be ready on defense. The veteran and team leader missed practice Wednesday and Thursday, but returned on a limited basis on Friday.
''We'll see how it goes,'' Ryans said. ''I'm just trying to get the hamstring right. Sometimes these things can take two or three, weeks to get right.''
Ryans suffered the injury in a 27-7 win over the New York Giants Oct. 19 and missed the team's loss to the Panthers. With him missing in the middle of the defense, the Panthers ran for 204 yards.