OXNARD, Calif. -- Following his daily news briefing with the media, coach Jason Garrett walked back to the practice fields to watch three offensive linemen workout.

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Injuries to the offensive line prompted the Cowboys to bring in Montrae Holland, Derrick Dockery and Daniel Loper on Friday afternoon.

Garrett said he's not sure when Nate Livings (hamstring), Mackenzy Bernadeau (hip and knee), Kevin Kowalski (ankle) and Bill Nagy (ankle) will practice again, which forced the Cowboys to bring in some more players to get snaps with the offensive line.

Holland and Dockery have started games for the Cowboys in the past and Loper spent last season with the team.

"We've got to get some guys in here who can play," Garrett said. "The young guys are getting a lot of work. One of our objectives of training camp is to evaluate players. We have a tremendous amount of plays of those young interior offensive linemen on tape already. So they're getting a chance to play different spots, see different looks, but we need to bring some guys in."

The Cowboys have juggled the interior of their offensive line in the first week of camp.

Kowalski was supposed to compete with Phil Costa for the starting center job. Instead, David Arkin and Harland Gunn are getting first- and second-team reps because of health issues.

Ronald Leary and Arkin are sharing reps on the second team at guard.

At some point the Cowboys have to get their offensive line together from a chemistry standpoint. The projected starters are: left tackle Tyron Smith, left guard Bernadeau, center Costa, right guard Livings and right tackle Doug Free.

The tackle and center spots are settled, it would seem, but Livings' injury this week has created problems.

"Continuity is always a challenge," Garrett said. "Regardless of how much time you play together, you always feel like you want more time, particularly on the offensive line. You like to get to that point as quickly as possible. Injuries are a reality in the NFL. You have to be able to deal with them. Injuries mean opportunities for young guys, and those guys have to step up and get in there and show us they can do something and make this football team and have a role on this team. It's a great chance for them, hopefully sooner rather than later."