The Philadelphia Flyers took a commanding 3-1 series lead over the New Jersey Devils following Tuesday's victory, but the win came at a cost.
According to the Flyers, Gagne could return to action in three weeks while Carter is out indefinitely.
Gagne blocked a Brian Rolston shot in the second period and was forced to leave the game with less than eight minutes remaining in the period. Carter was hit by a shot from the point by Chris Pronger, in which he immediately deposited the loose puck for his second goal of the game.
Carter, who led the team in goals with 33 in the regular season and has two goals and an assist in four playoff games, missed eight games towards the end of the regular season with a fractured left foot. Gagne has two assists in four playoff games.
The Flyers will try to clinch the series Thursday night in New Jersey (7:30pm et/4:30pm pt on TSN2).