Callahan, tied for second on the Rangers with seven goals, was injured midway through the first period and didn't return to the game.
He was checked by Predators defenseman Victor Bartley, who swung around and kicked Callahan's left leg into the boards.
Rangers coach Alain Vigneault said after the game that the injury was a second-degree sprain and provided the estimated recovery time.
Callahan was in pain on the bench and then went toward the dressing room 10:54 into the period. He played four shifts and totaled just 3:28 of ice time. He wasn't on the ice for either of Nashville's two first-period goals.
In 24 games, Callahan also has 13 points for the offensively challenged Rangers. He sat out the season opener following shoulder surgery and missed seven games between Oct. 19 and Nov. 2 because of a broken thumb.
Callahan, signed through this season, can become an unrestricted free agent in the summer.
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