EARTH CITY, Mo. -- St. Louis Rams offensive lineman Barrett Jones is out for the rest of the preseason and likely beyond because of back surgery, coach Jeff Fisher confirmed Sunday afternoon.

"Barrett is going to be weeks away," Fisher said. "Barrett has had some minor surgery on his back so he will not participate in the preseason. Beyond that, I don't know."

Late last week, we covered the Rams' lack of experienced depth behind the starting offensive line with mention of Jones' back injury. At the time, I was told that Jones would be out for "awhile." Anytime a back surgery is involved, it's probably best not to take a guess at a possible return. In fact, it's probably best not to count on Jones returning at all at this season.

Jones' injury, combined with rookie Demetrius Rhaney's knee injury suffered in practice last week leaves the Rams thin at center moving forward. Fisher said Rhaney had an MRI on the knee and the results were better than expected, though Rhaney is also going to miss a chunk of time.

"We got good news," Fisher said. "We suspected the worst but got good news. He has no ligament damage whatsoever. The cartilage looks good, solid, no cartilage damage. He's got a severe bone bruise I guess I would classify it and he's going to be out for some time. These things typically take time.

"I can't tell you whether it's going to be four weeks or six weeks but I would not expect him back within the four week time period."

Without Jones and Rhaney, the Rams have turned to versatile lineman Mike Person to provide center insurance. Scott Wells is working as the starter and Tim Barnes remains solid as the top backup but Person worked with the third team offense in the middle against Green Bay on Saturday. Person also played left tackle and left guard in the game, playing all 71 offensive snaps in the game.

While the Rams don't have to make any snap decisions on Rhaney or Jones, they did lose running back Isaiah Pead to a torn ACL and will likely have a roster spot open to replace him. That spot could theoretically go to an offensive lineman.

"I think we are good right now," Fisher said. "We've got depth, we've got flexibility. We're going to look. This is a time you typically continue to evaluate the bottom half of your roster and watch the waiver wire and we'll make room with Isaiah's spot. If somebody is out there we'll consider it but we're not looking to replace position for a position."