What is the likelihood of having a sour crop?

Oh no, it sounds like your feathered friend is feeling a bit under the weather! A swollen crop can indeed be concerning, especially when it's not hard to the touch and accompanied by lethargy. This could indicate a condition known as sour crop, where the crop becomes impacted or infected, leading to an accumulation of food and fluid. While it's great that you're planning a vet visit, it's important to monitor your chicken closely until then. Ensure he has access to fresh water and consider gently massaging the crop to help with any potential blockage.