Yes. PLEASE end it's suffering right away! (I have found that a sharp pair of shears is the fastest, kindest way for the chicky, cover everything with a paper towel so you don't have to see it and it'll be easier for you too).
I second this - be absolutely certain of what you are seeing before you cull. Can you show a pic?
ETA - If you do a search for baking soda & vinegar, this is a humane way to do this without having to go through the kitchen shears thing. The shears are also quick (if they're very sharp), but I personally don't think I could do it. I have done the baking soda thing.
Please listen to Silkiechicken, I've had a large-bellied chick before, sometimes they absorb a huge yolk, giving them a huge belly, to large to walk. Once the yolk is digested, the belly gets alot smaller. If you can, please post a picture of where the vent is/should be.