An Avian Vet visit is well worth your time to provide a precise determination.
As stated above, It does look like a Pressure Point problem that has resulted in the loss of the Pad Surface.
As recommended, changing out the current perches with Natural wood branches 'of size' will help to shift the location of the bodies weight.
Please visit the Amazon Forum and open the Sticky Thread, something like: I Love Amazons -... Look for the Segment that is titled: Getting to the Foot of the Problem. Your will find that Segment informative and very helpful.
Please assure that you visit an Avian Vet to obtain mediation to limit any bacteria .