My goodness! The poor thing! I would take it to a vet pronto. After you have taken him to the hospital take a look at these websites for a good reference:

Can I keep other aquatic life with my ACF?


African Clawed Frog Housing and Feeding


African Clawed Frog Disease and Injury


Disease & Illness


I hope he gets better. If he does not get better feel free to contact me. I will see what I can do if you need any help.