From the Washington Post:

Redskins running back Clinton Portis, who recently added a rib muscle strain to his array of injuries, is considered only “50-50″ to play Sunday against the New York Giants at FedEx Field, Coach Jim Zorn said yesterday. “There’s a chance he’ll be there,” Zorn said after practice at Redskins Park, “but he’s still questionable.” After sitting out practice Wednesday and Thursday, Portis “took some reps” today, Zorn said