Okung injured his left big toe blocking 49ers defensive end Justin Smith on the final play of the first quarter.
Coach Pete Carroll says Okung suffered a torn ligament in his toe and the injury is expected to keep him sidelined for six to eight weeks.
"It gives him a chance to come back," Carroll said. "It's a six- to eight-week injury and we'll hope that that will all work out right for us. He's determined, he's kind of excited about the fact that he has a chance to get back this season as well. So we will just ride it out, see what happens, and take good care of him and hopefully we'll be able to make it."
Under the injured reserve rules, Okung will be ineligible for the next eight weeks. He can return to practice six weeks after being placed on the list and be eligible to play against Minnesota on Nov. 17.
Paul McQuistan will start in place of Okung against the Jacksonville Jaguars. McQuistan started the first two games of the year at left guard for the Seahawks.
With McQuistan moving to tackle, James Carpenter will take over at left guard. Carpenter rotated in with McQuistan during the first two weeks. Carroll said Carpenter is ready to play a full game after getting back in shape from a foot injury that sidelined him during training camp.
The Seahawks also expect to see the season debut of two key pieces on the defensive side of the ball. Cornerback Brandon Browner and defensive end Chris Clemons are both expected to play against the Jaguars on Sunday.
Browner suffered a strained hamstring in practice two weeks ago and wasn't able to return to practice until this week. Browner is expected to start while the plan for Clemons will be more reserved.
Clemons is coming back from a torn ACL suffered in Seattle's playoff win over the Washington Redskins in January. Carroll said that they will monitor his reps in the game but he's in great shape and conditioning shouldn't be a factor.
"We're really, really thrilled for him," Carroll said. "It means the world to Chris of course, as he gets back. He had great preparation, he had a fantastic recovery process, the rehab, everything. So he has a chance to play for us this week and I'm really fired up that he gets to join us. We missed that."
Clemons has led the Seahawks in sacks in each of the last three seasons. He recorded 11 sacks in both 2010 and 2011 and 11.5 sacks last year for Seattle. Fellow defensive end Red Bryant says the return of Clemons will be a huge boost for an already imposing defense.
"He's a big part of what we do on defense. He's one of our leaders. We're excited for him to contribute with how hard he's worked to get back," Bryant said. "It's going to be big, man. We really can't put into words how excited we really are that he's back."
Notes: DT Jordan Hill was officially ruled out for the game with a strained biceps. ... FB Spencer Ware (ankle) and S Jeron Johnson (hamstring) are both listed as doubtful. Carroll confirmed Ware suffered a high ankle sprain last week against the 49ers. ... T Breno Giacomini (knee) and G J.R. Sweezy (back) are listed as probable. ... With the move of T Russell Okung to injured reserve, the Seahawks have an open roster that they expect to fill by Saturday.