He no sooner needs to have his foreskin cut off than he needs to have a foot taken off. I mean- it happens sometimes- but you don't just go volunteer. Why don't you try to think of something nice to say to him that reassures him that his foreskin is an important part of his body (as I am sure he feels already) and that unless there are problems and nothing else would help him, he should not even spend a minute of his day worrying himself over it. He needs to find a doctor who understands the value of a whole body and who would not treat him as if select parts are disposable.
(just in case I was not clear- some men with diabetes do have difficulty with yeast, infections and healing... what he has heard... it does happen sometimes, but hopefully he will be able to manage his condition and any problems that do arise if they do arise, without circumcision... so don't just pish-posh at his concern... it does happen)