RENTON, Wash. - Already saddled with two major losses on the offensive line, the Seattle Seahawks returned from a four-day break Tuesday with even more shuffling to do up front.

If the Seahawks haven't already reached their tipping point along the line of scrimmage, they may be at the edge.

"We're getting close now where new guys are going to have to play next," coach Pete Carroll said. "Hopefully we can keep everybody together and make a good finish here."

The latest changes are the result of left tackle Russell Okung being placed on injured reserve after tearing a pectoral muscle in Seattle's 31-14 win over Philadelphia last Thursday. That made him the third starting offensive lineman to go down in the last month. The Seahawks signed guard Mike Gibson to add depth, but the big changes concern the starters.

Paul McQuistan will move from right guard to left tackle to take over for Okung, Carroll said, while Lemuel Jeanpierre, who started at center earlier this season against Cleveland, will move in at right guard. Carroll was previously hesitant about moving Jeanpierre into the starting lineup because he is also the backup center. That role now falls to Gibson.

"The fact that these guys have been with us and we don't have to go outside the organization and the system to get guys means we're very fortunate," Carroll said. "It does speak to the depth that we started camp with, in terms of familiar faces, anyway, instead of having to go some other way. Hopefully this'll work out and we'll be able to keep going."

Okung got thrown by Philadelphia defensive end Trent Cole away from the play inside the final 2 minutes and after the whistle had blown. Okung underwent tests last Friday when the injury was diagnosed. He and Cole engaged on a run by Leon Washington that went to the right side. On the television broadcast, Okung appears to let up as the whistle blows, then gets flung over Cole's hip and to the ground.

Okung had to be restrained and pulled away from Cole after the game ended.

Seahawks center Max Unger was one of the first players to see what happened and rushed over to Okung.

"It was a bummer, man. It was just a bad play, both sides," Unger said. "I guess we really wouldn't be talking about it unless Russ tore his pec."

The loss of Okung was the third blow to Seattle's offensive line in just a few weeks. They said goodbye to rookies John Moffitt and James Carpenter within days of each other, both due to season-ending knee injuries. Moffitt tore two ligaments in his right knee during Seattle's Week 10 victory over Baltimore, while Carpenter went down a few days later in practice and is out with a torn ACL.

To add further indignity to Moffitt's shortened season, he was suspended four games by the NFL on Tuesday for violating the league's policy on performance-enhancing drugs. Moffitt will serve the suspension, without pay, while on injured reserve. His agent, Michael George, said Moffitt was suspended for not getting pre-approval for taking the prescription drug Adderall, which is for hyperactivity.

The Seahawks didn't appear to miss a step with Carpenter and Moffitt out for the year. They continued to find success running the ball with Marshawn Lynch in victories over St. Louis and Philadelphia, sandwiched around a loss to Washington in which the Seahawks had a 17-7 lead with 12 minutes remaining. Seattle has topped 100 yards rushing in five straight games, its longest streak since the 2005 season, when Seattle won its only NFC championship behind the running of Shaun Alexander.

If Seattle (5-7) can top 100 yards rushing again Monday night against St. Louis (2-10), it would be the longest single-season streak for the team in 15 years.

"I'm very proud and happy that they have the faith in me to go in there and step in. I just have to go out there and work my butt off and prove them right," Jeanpierre said.