I'd go and get it checked out if it were me and I'd say the same to anyone, whether they have diabetes or not. Actually, it's even more important to get a non-painful injury checked, if you have any changes in sensation - diabetic neuropathy. In the meantime, first aid for any bone / muscle injury is RICE rest (keeping weight off), ice, compression (although not if broken bones suspected), elevation (raising to reduce swelling).