No timetable was given for his return, but the Seattle Times reported he is expected to have season-ending surgery.
The injury happened within the final two minutes of the game when Okung was tossed to the ground by Eagles defensive lineman Trent Cole after the whistle had blown.
"He got thrown down after the whistle, really blatantly," Seahawks head coach Pete Carroll said. "Stuff like that happens in the game sometimes, but this was most unfortunate because he was damaged by it."
Okung, the sixth overall pick in the 2010 draft, started 10 games last season while battling a couple ankle injuries and had started all 12 games this year.
He is the third Seattle offensive linemen to be lost for the season, as the Seahawks had already lost James Carpenter and John Moffitt to knee ailments.