Its the egg yolk! Be careful cause sometimes when they dont lose it, it can be deadly... Ive had several ducks die like that but ive never hatched chickens so we'll see!
It's the yoke, keep it by it's self on a towel with heat and everything that a chick needs. I've had it happen before and now she's a pretty hen. They still can absorb their yoke the rest of the way. Hope your chick does as well as mine did.