Kovalchuk, who had a pair of assists, two shots on goal and a plus-2 rating -- he set up both New Jersey goals in the second period -- left the ice for the final time with 1:35 left in the third period. He sat out all of overtime and was unavailable for the shootout, which the Devils won on goals by Zach Parise and Patrik Elias.
SOG: 40 | +/-: -5
The Devils don't play again until Saturday, when the Winnipeg Jets visit the Prudential Center.
When asked if he was concerned about the injury, Kovalchuk said, "I never got it before. We've got good doctors and we'll see what they're going to tell me (Friday)."
Kovalchuk said he thought about going out in the shootout, but said, "I tried and it wasn't good at all."
Kovalchuk wasn't the only player leaving Philadelphia at less than 100 percent.
Goalie Johan Hedberg told reporters his back was stiff and he had to sit while speaking with the media.
"Something popped in my back in the middle of the third," he said after stopping 20 of 23 shots. "The good thing was my crouch was the position that felt the best. That was the best position to stay in. So it should be fine (Friday). Right now, I'm a little stiff."
Defenseman Andy Greene was a late scratch from the lineup. Coach Peter DeBoer said Greene had a lower-body injury, and after playing 18:47 Wednesday against Toronto, he was given Thursday's game off. Mark Fraser played in his place.
Contact Adam Kimelman at firstname.lastname@example.org. Follow him on Twitter: @NHLAdamK