I had one hatch with the yolk sac exactly like that. It won't absorb. The yolk sac is completely external, there's no way for the chick to absorb it. I wrapped the whole thing, chick and yolk, in a wash cloth and tucked it into a coffee mug in the brooder. The mug immobilized it and protected it from the other chicks while the umbilicus dried. The yolk sac burst and I was able to cut the whole mess off the chick because the cord was dry by then. I tucked it back into the mug to rest and an hour later I looked in there and the chick was standing beside the mug. She was a skinny little thing because she hadn't absorbed the yolk, but she did just fine. She's out in the run right now, you'd never know she had a problem when she hatched.