Coach Jack Capuano provided the update before Saturday's game without saying what the injury was. De Haan did not return after being hit by Troy Brouwer in the third period of New York's 5-1 loss Thursday.
The Islanders trail the first-round series 3-2 and are already without two other defensemen. Travis Hamonic has not played since the next-to-last game of the regular season. Lubomir Visnovsky sustained a head injury in Game 4 on Tuesday.