OXNARD, Calif. -- The Cowboys have center issues. With Phil Costa having health issues, it raises a few more questions about the offensive line.

Who plays center?: We don't know the extent of Costa's back injury, but the Cowboys have been cautious this summer when it comes to players returning from injuries. Costa has two days to get better in time for the preseason opener, but you have to wonder if David Arkin will get the start at Oakland. Arkin received some first-team snaps with Costa out Friday. If Costa misses practice again, it's a given Arkin will get first-team reps. Harland Gunn also received some snaps and it wouldn't surprise anyone if Mackenzy Bernadeau got some snaps at center against Oakland if Costa misses the game.

Hanna gets his shot: With John Phillips out with an ankle sprain, rookie tight end John Hanna has received more snaps with the first-team offense. Hanna is a better pass catcher than Phillips, but Phillips is the better blocker. The Cowboys want to see Hanna improve his blocking, especially out of two-tight end sets.

Defensive line battles: Most of the talk has been about the No. 3 receiver job, but the Cowboys have some battles going along the defensive line. Jay Ratliff and Jason Hatcher appear locks to make the roster. Defensive line coach Brian Baker said Sean Lissemore has starter talent, and Kenyon Coleman and Marcus Spears have started plenty of games in this league. Josh Brent is getting snaps at nose tackle and defensive end, and Tyrone Crawford has moved up the depth chart to the second team with the injury to Hatcher and has caught the coaches' eyes. Baker said he's impressed with how strong Crawford is against the run, something the Cowboys thought he might need work on. Robert Callaway and Ben Bass are long shots to make the roster. The game at Oakland will tell a lot about this group.

Deep snapper: L.P. Ladouceur and Charley Hughlett will handle the long snapper duties Monday night. Watch out for Hughlett because with Ladouceur in the final year of his deal, the Cowboys might find their future deep snapper.

If you're here: Jason Garrett talks at 2 p.m. CT and the practice starts at 4:30 p.m. CT.