There has been yet another changing of the guard — literally — on the Seahawks’ offensive line, with starting OLG James Carpenter being unable to finish his second consecutive season after injuring his knee early in the Week 13 victory over the Bears.

Carpenter was placed on the reserve/non-football illness list on Tuesday after what was widely considered Seattle’s biggest victory of the season. But team sources are guardedly optimistic that John Moffitt — who started two games at right guard early in the campaign as well as two recent games at left guard when Carpenter was out with a concussion — will be an adequate enough replacement.

“He’s been OK, some good, some bad,” one source said of Moffitt, who was initially envisioned as the team’s right guard for a long time to come alongside Carpenter at right tackle. “Carpenter is a real road grader. When he pushes out, he just covers up guys. Moffitt’s not quite as physical, but he’s more mobile with better quickness, and that could help from a pass-protection standpoint.”

Taking over the swing guard role that Moffitt had been filling is rookie J.R. Sweezy, who did enough in the preseason to earn a starting role at right guard over Moffitt in Week One but quickly proved to be in over his head in the season-opening loss to the Cardinals.

“Arizona showed him stuff that he had never seen before,” the source said of Sweezy, a converted defensive tackle. “The team seems to think he now has a better grasp of the system.”

In the meantime, after starting the first three games at left guard, seventh-year veteran Paul McQuistan switched over to right guard in Week Four and has done a solid enough job to probably figure as a fixture at the position for the foreseeable future.