Cowboys center Phil Costa has a left knee injury that kept him out of practice Wednesday, a that's a concern considering backup center Ryan Cook is also banged up. (US Presswire)

The Cowboys had been without center Phil Costa for a while this year but were happy to have him back last Sunday in Baltimore.

Dallas ran the ball for a season-high 227 yards against the Ravens' defense in Costa’s first game since a back injury flared up three plays into the regular season.

But Costa is back on the injury report -- this time with a left knee injury that kept him out of practice Wednesday. The Cowboys officially listed him as “limited” but with backup center Ryan Cook (hamstring) also banged up, the team had to use David Arkin at center during practice.

Cook filled in nicely for Costa with three starts and there was some question about whether he would continue to start when Costa returned. But Cook’s hamstring injury made that an easy call for the Cowboys, who will certainly stick with Costa as the starter, if he’s healthy enough.

Also figuring into the mix could be Kevin Kowalski, who is set to return from the PUP list in the near future. Kowalski has been out with a high-ankle sprain since the start of the regular season. He filled in at guard and center last year as a rookie and was expected to compete for a starting job in camp before his injury.

Johnson’s debut close: The Cowboys are hopeful that rookie safety Matt Johnson will be able to play for the first time this week against the Panthers. Johnson has been sidelined by a string of injuries and unfortunate situations since he was drafted in April. Lately, Johnson has been out with a hamstring injury he suffered late in the preseason. That was after another hamstring injury that kept him out a month leading up to camp. And don’t forget that Johnson missed all but one offseason practice due to ineligibility because his classes at Eastern Washington were not completed until mid-June.

Johnson is expected to contribute on special teams, but possibly in defensive sub-packages.

Change at KR?: While Jason Garrett said he expected Felix Jones to get a few reps at kick return, although he’s expected to start for the injured DeMarco Murray (foot sprain), don’t be surprised if rookie Lance Dunbar takes over the job. Dunbar split reps with Jones last week and will likely get more with Jones having an expanded offensive role.

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