Carriker, the sixth-year defensive end, suffered a quad tendon tear and won't see the field again in 2012. Both players are scheduled to undergo surgery this week.
The news is especially painful for Orakpo, whose 2011 season was cut short with a similar injury. He aggravated the pectoral muscle again during the preseason and never appeared 100 percent healthy.
Sunday's setback was initially viewed as a week-to-week situation, but the Redskins now must move forward without their most dynamic pass rusher.
"He can do it all," Shanahan said of Orakpo. He's everything you look at in a Pro Bowl linebacker."
Shanahan, forced to turn the page, named backup defensive lineman Chris Baker and practice-squad body Doug Worthington as candidates to step into a larger role in Carriker's absence.
Follow Marc Sessler on Twitter @MarcSesslerNFL.