The Rangers, beaten by the same score by the Flyers on Thursday, lost Callahan early in the third period when he was injured during a tussle with Philadelphia's Maxime Talbot.
Callahan skated straight off the ice and did not return. The injury would be evaluated further on Wednesday, the team said.
"We were holding each other up and his shoulder popped out or something," Talbot said. "It was unfortunate. I let him go. I kind of felt it, but then I saw his face as well."
After trailing 2-0 by the second period, the Flyers pegged back a goal in the third through Kimmo Timonen, who converted a power-play.
But the visitors could not find an equaliser as New York killed off a pair of power-plays and goaltender Henrik Lundqvist made 26 saves.
"It was really big," said Rangers coach John Tortorella of his team's defensive effort. "We've been on the other end of it, not scoring (on power-plays). It's an important part of the game."
New York had built an early cushion courtesy of Michael Del Zotto who scored in the first period, then assisted on Callahan's goal in the second to give the Rangers a 2-0 lead.
The victory was New York's (3-3-0) third in four games following a slow start to the season. Atlantic division rivals Philadelphia (2-5-0) have now dropped two straight.
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