Karlsson sustained a lower-body injury versus the Ducks on Saturday, Jesse Granger of The Athletic reports.
Head coach Bruce Cassidy estimated that Karlsson is in the day-to-day range, but any official update won't come until Monday at the earliest, as the Golden Knights will not practice Sunday. That leaves Karlsson in doubt -- but not yet ruled out -- for Monday's contest versus the Panthers. Alexander Holtz is likely to enter the lineup if Karlsson can't play, while Brett Howden would likely shift from the wing to center.