OXNARD, Calif. -- The Cowboys expect backup offensive guard Marcus Martin to miss the rest of the season with a torn ligament in his right big toe.

Martin suffered the injury Thursday in the preseason opener at San Francisco. Martin is seeking a second opinion from another doctor before deciding whether or not to have surgery. Regardless if he has the surgery or not, he's still expected to miss all of the 2018 season.

The Cowboys signed Martin to a one-year deal in free agency this offseason to give them more depth along the offensive line. The Cowboys had been concerned with his conditioning early in training camp and had him working on the side during some of the early practices. Martin hasn't played in a regular-season game since Dec. 18, 2016, while playing for the 49ers against Atlanta.

But Martin figured to land one of the reserve offensive line positions on the final roster. Now, the Cowboys are left with veteran Joe Looney as one of the only key reserves up front. Looney has been the second-team center in team drills in training camp but can also play guard.

After Martin's injury, the Cowboys have had Kadeem Edwards (6-4, 315) playing at second-team right guard and Dustin Stanton (6-6, 310) at second-team left guard.