What could this be?

[EnesaMac]

Hi, I picked up my 4 week old buff orpington and noticed this what felt like an air filled pocked. I have attached pictures below.
Its on the right side only. S/he is eating and drinking well

 

[HKG]

@Eggcessive

 

[HKG]

I think it looks like a ruptured air sac.

 

[coach723]

It does look like a ruptured air sac. It can happen from running into something, or with small chicks from getting knocked around. It may resolve on it's own. If it does not, or continues to get larger, or the bird has difficulty breathing, then releasing the air takes the pressure off the air sac and may allow it to heal. Wipe the skin where the air is with antiseptic, prick the skin with a sterilized sewing needle (Pinch the skin and push the needle through the pinch, just under the skin). Let the air escape and then apply a dab of plain antibiotic ointment, like neosporin. Sometimes it may need to be repeated if it fills again.