Isolate the animal, wait 24 to 48 hours from hatching and if within normal size range assist feed a large fuzzy mouse (pinky will not make a difference), than wait and see, it will either regain strength or fail to thrive). If it makes it you can offer food again when the others start feeding. I do not mention shed because it is possible this animal does not shed as expected but take much longer and therefore you do not want to go by that.