Coach Jim Zorn said Portis will be a game-time decision, although Portis has given every indication that he will play. He ran for 68 yards on 15 carries in last week's game against the Dallas Cowboys despite not practicing at all.
"Clinton is game-time because he's really not full speed," Zorn said.
Receiver Antwaan Randle El is also questionable with a sprained ankle.
"He was a little ginger," Zorn said, "but I think by game time he'll be ready to go."
The Redskins flew to Seattle after practice to give them a full day to recover from the long flight before Sunday's game.