IRVING, Texas -- It's been a tough start for the professional career of Cowboys safety Matt Johnson.

The rookie missed offseason work because his college, Eastern Washington, was still in session, then a hamstring injury in training camp slowed his development when he finally was ready to practice.

Johnson's hamstring injury has lingered, and coach Jason Garrett revealed Monday the rookie also has a back problem. Garrett said Johnson injured his back while rehabbing from the leg injury.

It appears this could be a lost year for Johnson, and it's only going to sting more because of the season-ending injury to starting safety Barry Church (Achilles). With Church out, the Cowboys could have given Johnson some snaps in a backup role on defense. Instead, the team will try and sign a free agent.

Mario Butler, a cornerback/safety, cleared waivers Monday after the Cowboys cut him Saturday and is eligible to be re-signed. A decision hasn't been made regarding the safety position yet, but when Church officially goes on injured reserve, the Cowboys will have one available roster spot.

Gerald Sensabaugh, the other starting safety, missed Sunday's game with a calf injury. With the next game being Monday night, he gets an extra day to recover. Sensabaugh said after the Tampa Bay game that he's fine.

Garrett said he didn't think the safety position was in trouble, but he has five safeties on the roster with three of them injured.