An MRI on Wednesday revealed that Callahan has a partially dislocated left shoulder.
"Definitely could have been a lot worse than it was," Callahan said Thursday in a video posted on the Rangers' website. "After the MRI, we got news there was no structural damage, so it's just a matter of a little bit of rehab, get some treatment and get back at it."
Callahan suffered the injury during a fight with Maxime Talbot in the third period of Tuesday's 2-1 win over the Philadelphia Flyers. Callahan said he doesn't know how the injury happened as he got caught in a wrong position while the two were pushing and pulling.
Callahan knew immediately that something was wrong and quickly left the ice, favoring that shoulder as he skated off. He applauded Talbot for recognizing he was injured and letting up during their tussle, and doesn't believe that the surprise nature of the fight contributed to the dislocated shoulder.
"Any time you miss time, especially in a shortened season like this, it's hard," Callahan said. "I wish I was out there, but at the same time, injuries happen during the year and these things are going to happen and it's just a matter of trying to get back as quick as I can."
While he injured the shoulder fighting, Callahan has no hesitation about dropping the gloves again.
"It happens. It's a freak thing," Callahan said. "I got caught in exactly the right spot to have this happen, and fighting, or whatever it may be, is part of the game and if it presents itself again, you have to do it."
After Callahan pulled Talbot out of a pile in front of the net, the Flyers forward dropped his gloves and went right at Callahan.
"Just unlucky, I guess," Callahan said Thursday.
Callahan, 27, said the next few days will focus on allowing the inflammation to settle down, and then he and the Rangers' training staff will focus on getting his shoulder stronger through treatment.
Callahan said he currently isn't in too much pain, although the shoulder flares up if he moves it too much.
The recovery timetable means he could miss between four to seven games. If he only needs 10 days, he could return against the Tampa Bay Lightning on Feb. 10. If he misses the full two weeks, that could mean a return in a home game against the New York Islanders on Feb. 14.
Callahan last missed an extended amount of games in 2010-11, when he played just 60 after breaking his hand and fracturing his ankle right before the end of the season.
He has two goals this season, both on the power play, and will be sorely missed over the next two weeks. He's on the Rangers' second line, is great on the penalty kill and has proved to be the team's top scorer this season on the power play.
"He's a huge part of our team," Rangers forward Derek Stepan said. "But everyone is going to have to step up, take a little bit of his pie and try to do some of the things he does. It's going to take six, seven, eight guys to fill the role that Cally does."
Added center Brad Richards: "Hopefully it's short and he gets back quick. Obviously the mood around here is we want him back as soon as possible. Big part of every part of the game. Power play, penalty kill, 5-on-5s. That being said, we've got to push on. It's part of the game we play."
One player the Rangers hope will step up in Callahan's absence will be Stepan. While he's fifth on the team with four points, he has yet to score a goal. One of the Rangers' problems this year has been a lack of production outside their top line of Richards, Rick Nash and Marian Gaborik.
"You lose a top guy like that, it shuffles the lineup. Gives other guys chances they probably wouldn't get if he was playing," Rangers coach John Tortorella said Wednesday. "I feel comfortable in us joining together as a team and trying to get it solved until we get him back."
"Individually I'm still working on my game; I still got a lot to sharpen up," Stepan said. "I think now with Cally out it's going to be most important to really get it straightened out now."
The Rangers also will be without forward Chris Kreider for Thursday's game against the Penguins as he recovers from a bone chip in his ankle. He had a light skate Wednesday and also skated Thursday morning, according to reports.
Matt Ehalt is a regular contributor to ESPNNewYork.com.