I can only go on personal experience and what you've written here:
It doesn't sound to me like he has anything wrong other than problems that he had before coming into your care. The listlessness and pale color are, most likely, from being in the cold and stress from a new environment.
Is he missing any scales? Right now, I just advise you to keep an eye on him for the next few days and keep him warm. As has already been suggested, keep things a bit dark;maybe put a towel over his tank to minimize stress for the next 24 hours, maybe longer depending on how he's doing. Stress coat is also wonderful for fin regrowth and for helping to minimize stress.
I had something similar happen with one of my previous fish, Raphael. It's a long story- but I had to get his tank out of a place I was living at the time on short notice. I actually had to have someone go into the house and bring the tank out to me. It was a bad situation, and I speed away from the house; by the time I had composed myself enough to slow down and check on Raphael, his tank was on it's side and the poor dear was on my dirty car floor. That fish was bionic, because he didn't even have a scratch on him after that.
And last but not least, kudos to you for stepping up and taking care of him!
Pictures would be helpful, but I wouldn't stress him out with a photo shoot just yet. Best of luck with your new little one!!