Russell Okung left the Seahawks' victory over Philadelphia on Thursday in the fourth quarter with what coach Pete Carroll described as a significant pectoral injury.

Okung suffered the injury while engaged with defensive end Trent Cole, who continued wrenching on Okung's arm.

Okung starts at left tackle, which is considered the most important position on the offensive line. He was Seattle's first-round draft pick in 2010, the No. 6 overall choice.

There is no final diagnosis on the severity of the pectoral injury, but it can be an injury that requires season-ending surgery. In the locker room after the game, Okung was holding his arm completely stationary, and had to have his uniform cut off of him.

He is the third Seahawks starting lineman to suffer a significant injury. Starting right tackle James Carpenter and right guard John Moffitt suffered season-ending knee injuries in the span of a week last month.

If Okung is unable to play, Seattle would be scrambling for a replacement. Breno Giacomini is starting at right tackle, and the only other tackle on the roster is Jarriel King, who has recently worked at guard.

Seahawks players will be off until Tuesday, so it's unclear when there will be an update regarding Okung's status for the final four games.

Danny O'Neil: 206-464-2364 or doneil@seattletimes.com.

On Twitter @dannyoneil