hi, i would suggest you need to take your husband urgently to be seen by a physician as it could be that blood is not flowing properly in the affected leg, it could be dvt, vasculitis
, could be an infection of the skin or fat beneath called cellulitis
, he needs to be investigated throughly and put on treatment as soon as possible to avoid complications if diabetic we could be dealing with vasculitis or even gangrenous foot. so my suggestion would be to take him to the physician asap.
hope have been able to answer your query.