OXNARD, Calif. — The Cowboys had high hopes for Matt Johnson when they drafted the Eastern Washington safety in the fourth round in 2012. They have held onto those hopes, despite the fact that he has never played in a regular-season game.Seeking an explanation for recurring hamstring injuries, Johnson returned to Dallas to see a back specialist Thursday."Matt is going to see a back specialist in Dallas today to see if that relates at all to his hamstring situations, so we feel like he’s making progress, and hopefully we can get him back soon enough where he can show us what he can do in a game," Cowboys coach Jason Garrett said. "Just turning over all the rocks."Johnson rarely has practiced in his three seasons, because of back, foot and primarily hamstring injuries. He reinjured his hamstring in a July 29 training camp practice, and an MRI revealed a strain. He had been expected to miss a week but has yet to return to practice.