It is fairly common to have a chick born with an umbilical cord that has not fallen off. I would put him back in the incubator, and when you do remove him when he is dry and feathered out, just check him in the brooder often so that the other chicks don't peck it and make it bleed. It should start drying out and shrinking a little each day. Most are gone within a week. Just look at the chick's vent to make sure it is open, and that this piece of tissue is the umbilicus.
I just meant to check that this red thing isn't coming out of the vent. If the other chicks peck him, you may have to put a little something to separate him in the brooder like a little divider.