Is the chick getting pecked at? Other chicks will peck it until it bleeds and cause extreme problems for your flock (bad habit of pecking).
I would put Rooster Booster Pick no more lotion on it if you have it to prevent pecking. It stains and looks like molasses- they should have a no-pick salve at the feed store. They don't like the taste.
Another good thing to put on it if you don't have no-pick lotion is antibiotic ointment without painkillers. And if you don't have that, then vaseline might help.
I have had pasty butt that I wash off, then the area is reddened slightly from cleaning. Then other chicks start pecking unmercifully at it until it is bleeding. That's why I mentioned the no pick lotion...but if you are not experiencing that, then the antibiotic ointment should be great.
You can even separate the little guy inside the brooder with food and water until you get some no pick lotion if they start cannibalizing.