Demko left Thursday's game versus the Kraken due to back spasms, Brendan Batchelor of Sportsnet 650 reports.
While it's not an encouraging update, it's far from a worst-case scenario, which would be a recurrence of his knee injury. Demko can be considered day-to-day for now and likely won't start versus the Predators on Friday, though it's unclear if he'll be healthy enough to back up in that contest.