The Seahawks added depth at running back Tuesday, signing rookie Bo Scarbrough off of Jacksonville's practice squad. He replaces guard Jordan Simmons, who was placed on injured reserve due to a knee injury sustained in Sunday's game at the San Francisco 49ers.

Simmons, who the Seahawks claimed off waivers prior to the start of the season, started three games this year in place of an injured D.J. Fluker, including Seattle's top two rushing performances of the season when the Seahawks rushed for 273 yards against the Rams in Week 10 and 214 yards in a Week 14 win over the Vikings.

The addition of Scarbrough comes after the Seahawks played without rookie running back Rashaad Penny in their Week 15 loss to the 49ers. Asked on Monday about the status of Penny, who missed Sunday's game with a knee injury, Seahawks coach Pete Carroll said, "We've got to wait a couple of days here. We'll see by Wednesday. He's working hard to try to get back, but it's not certain yet if he's going to be able to turn it around or not."

Scarbrough, a two-time National Champion at Alabama, was selected by Dallas in the seventh round of this year's draft. After being waived by the Cowboys prior to the start of the season, he then signed to Dallas' practice squad. Scarbrough, who is 6-foot-1, 235 pounds, was signed to the Jaguars practice squad in October after being released by Dallas. In four preseasons games with Dallas, Scarbrough carried 24 times for 69 yards and one touchdown.