Foot ulcers in diabetics are usually a reason to get in touch with a medical professional. Not something to keep walking around with (if one can even walk with them), it's something to get looked at as fast as possible. They can get out of hand when blood sugar control is poor, and/or if there's neuropathy present, so... Not a wait-and-see kind of thing. If it's bad, try ringing 111 and ask whether you should go to A&E.