Penny suffered a left ankle injury during Sunday's game in New Orleans, Brady Henderson of ESPN.com reports.
Penny picked up the health concern on a carry during Seattle's first possession of the second half and needed a cart to get to the locker room. If he's unable to reenter the contest, he'll come out of Week 5 with eight rushes for 54 yards. Rookie second-round pick Kenneth Walker and DeeJay Dallas are the remaining healthy running backs on the active roster.