Callahan, who has one of New York's 13 goals in eight games this season, was injured Tuesday night at Pittsburgh in the Rangers' second consecutive 1-0 defeat. An MRI taken Wednesday revealed a Grade 2 sprain that won't require surgery.
The Rangers have gotten off to a 2-5-1 start, and surprisingly the lack of offence is a big reason for their troubles. New York has dropped four straight, including back-to-back 1-0 losses for the first time in the club's 82 seasons.
New York is already without Martin Straka and agitator Sean Avery up front. Straka broke a finger Saturday at Boston and is expected to be sidelined four weeks, and Avery still has another seven to 10 days to recover from a shoulder injury that has limited him to two games this season.
It is the Rangers' smallest goal total through the first eight games since they had only nine in 1950. New York has gone 181 minutes, nine seconds without scoring an even-strength goal.
Callahan, 22, doesn't have any assists this season. He had four goals and two assists last season, playing 14 games in his first NHL campaign.
The Rangers, returning from a three-game road trip that produced one point, begin a six-game homestand Thursday night against New Jersey.