OXNARD, Calif. -- With all the discussions about tight end Jason Witten missing the rest of the preseason with a slightly lacerated spleen, starting center Phil Costa most likely will miss the second preseason game at San Diego with a strained lower back.

Costa missed the preseason opener at Oakland after injuring his back late last week. David Arkin took the majority of the snaps in the Raiders game until being replaced by Harland Gunn in the fourth quarter.

"Costa is getting better," coach Jason Garrett said Wednesday. "He probably won't practice today or tomorrow. He has a little bit of a back injury that he's dealing with. He is one of those tough guys that will lay in front of the train (before taking himself out of practice). We got to make sure we do what's right for him as well. He's progressing and feeling better and we're hopefully to get him back sooner rather than later."

The center position has been a mess for the Cowboys this training camp. Kevin Kowalski and Bill Nagy were supposed to compete for the starting gig with Costa. Injuries to Kowalski and Nagy allowed Costa to remain the starter.

But finding a backup has been a problem.

Arkin struggled with his snaps during training camp but had no such problems against Oakland. However, he was called for holding and allowed a first-quarter sack.

"Arkin did a fairly good job in the game and as you guys know, he's never played center before and you see some of the result of that in practice," Garrett said. "Some of the issues we have with the football. That was line one for him in the game is to take care of the ball. I thought he did a good job with that and he did a good job with the exchanges with the quarterback under center and also with the shotgun snaps. There's a lot for him to learn off of that tape."