You are experiencing bumblefoot infection caused by staphylococcus bacteria that enters the feet through any scratch or cut . Kindly inspect the bottom of the feet for any pus. If no pus, it is early stage that you can manage by soaking the feet in Epsom salt solution ( buy at any agrovet shop). In case of pus , you will have to perform surgery to remove the pus , clean with hydrogen peroxide and swab with 10% povidone iodine. Prevent this condition by maintaining clean litter free from sharp objects, have your patches with round edges.