Hi there....can you get a closer pic of the foot itself ? Is he with another beardie that may have bitten him ? Is there a small piece of skin shed around it ? If there is skin around it, it would be cutting off circulation. If that's the case try some raw honey on it [ from health store, not the normal grocery store type ] or put some plain aloe gel on it. Then see if you can very gently get the skin off once it's softened if that's the problem.