Seahawks HC Pete Carroll said after Sunday's game that RB Rashaad Penny's ankle injury is "serious," according to Greg Bell of the Tacoma News Tribune. Carroll also reportedly said it will be "very tough" for the team to get him back. Sounds like this might be a season-ender. We'll watch for further updates.
Update: NFL Network's Ian Rapoport reports that it's a fractured tibia, with tests coming Monday to asses to level of damage and whether he'll need surgery.