My African Grey had a case of bumblefoot when I got him and an ointment my vet prescribed cleared it right up. Providing the proper perches kept him from getting it again (his previous home only had dowel perches in his cage).
That definitely looks like a hotspot (pressure spot) to me. Does it seem to hurt him? This suggests a problem with perches or a problem with legs and feet.
It might not quite be bumblefoot but that’s the sort of change that leads to infection. Good job noticing this!
My Quaker had a bad leg and I needed to check her feet regularly; she would get hotspots and then an infection. She had lots of vetwrap per perches, and a big variety of perches that she could rest her tummy on and not have to hold with the bad foot.
Dowel perches put the same pressure in the same spots on the feet. This is why it’s important to have a variety of perch sizes.
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 .