I can’t be positive since there is no picture, but it sounds like pretty early stages of sore hocks. Does it look similar to this photo? :

… If so, it is early stages. The picture is actually one of my rabbit’s, who I am currently going through measures to ensure the hocks do not continue to deteriorate. If the blister is open or bleeding, then vet attention is needed, in addition to environmental/lifestyle changes.

Some things that can exacerbate/worsen sore hocks are:
1. Rough, abrasive, slippery, or wire flooring
2. Being overweight
3. Being inactive (i.e. keeping weight on hocks for elongated periods of time due to not moving)
4. Nails being too long
5. Exposure to wet flooring (ex. soiled litterboxes)

… If there any improvements you can make in these factors, that may help. Dr. Dana Krempels explains how to make a booty for rabbits who have more severe sore hocks (my vet assessed that my rabbit’s hocks were not advanced enough to need wrapping): http://www.bio.miami.edu/hare/sorehocks.html … if you do foresee not a lot of movement on that foot, a booty might be helpful, but you definitely do not want one over an open sore, as she mentions.

For example of changes, I changed the flooring in my rabbit’s overnight cage to 0.5in memory foam covered in a fleece material. I also have limited his pellets since the vet noted minor weight gain that might be contributing (he’s a netherland dwarf, so a slight increase might still be significant) and try to get him to move around more.

In terms of medical treatment, I have started doing a small application of silver sulfadiazine on each hock. It is a very small amount so it doesn’t stay moist, and I use a q-tip to gently apply it and work it in.

Rabbits can develop calluses on their heels. The callus can become red and irritated, which is the early stages of a sore hock but it isn’t quite there yet. Wick provided a good photo and advice on ways to help it heal.