This previous summer one of my imported red eye tree frogs had that exact same symptom show up. I removed him in his own 10 gallon tank with paper towel substrate, and gave him baytril drops on his his back until it disappeared. After about a week it went away but I continued the drops for 10 days as advised to me by Dr. Frye. He is all better now and doing just fine.
I would advise sending him a pic with a description of your problem immediately.
Last year I had a black RETF with the same bump. I took it to the vet and he irrigated it with a needle. There was infection inside. We gave it Baytril for 10 days. After irrigating the hole got larger and I was sure I would loose her. She survived and I have tadpoles in the water from her.
Okay, so I got the baytril from Dr. Frye and started applying it last night. One drop per day for 10-14 days. Hope this thing goes away, it would really suck to lose this frog since I've raised it since it was a baby. Dr Frye also gave me a de-wormer that I administer by dusting crickets with the powder. He said that could also be the cause of the issue. But I think that two people posting the exact same symptoms and the exact same cure means this will probably be resolved by Baytril.
On the plus side, this frog is still eating. Watched it own 3 crickets last night in a matter of 2 minutes, which is a relief.
I started applying the Baytril on Wednesday, and tonight (Saturday), the bump just popped. It's not bleeding or anything, and the hole isn't huge, but what now? The frog seems totally fine, and I found the gunk that was inside and cleaned it out of the tank just in case.