It looks like a bacterial infection. To prevent any further problems, isolate the frog in a hospital tank and follow this treatment schedule: ACFs can spend quite a long time out of the water as long as they are kept moist. Place frog in a hospital tank without water and swab infected area with BACTINE. Wait 20 minutes and place frog back into the hospital tank with water. Repeat twice daily until clear. Change water each time. If the red spots begin to cover the legs and thighs, then it becomes a much more serious problem, like "red leg".