Yes it looks like the start of neon disease.
If it is neon disease, you want to get the fish out asap and start treating it with antibiotics. The disease will be in the main tank and you should do a 75% water change and gravel clean the substrate every day for a week to dilute the disease organisms in the water and reduce the risk of other fish catching it. If other fish do get it, treat the main tank.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.
If you have 2 fish nets it's a lot easier to catch fish. Get a 5-6 inch net and a 8-12 inch net (depending on tank size). Put the big net against the front glass and rest the bottom of it on the substrate. Use the smaller net to guide the fish into the big net. Then lift it out.
