Fellow forward Jordan Eberle was also listed as day-to-day with an upper-body injury.
The Islanders were routed 5-0 at home by the Bruins on Tuesday to fall behind the Capitals in the Metropolitan Division.
Losing Filppula and Eberle for an extended period would hurt a team that already struggles to put the puck in the net. Filppula, 35, has 15 goals and 29 points this season. Eberle, 28, has 14 goals and 31 points.