Are his toe nails digging into the side of his toe (my husband has this issue) and it makes them very tender, but if you look at his toes you wouldn't know.
Idea: Trace his foot on a piece of cardboard, and stick it in his shoe see if he is getting a pressure point somewhere.
(Is it only when his shoes are on???)
Another idea:
Ask him if he wants a band-aid. Get him a special box of band-aids, let him pick out the box. (pick out two and let him point to the one he wants for his toe)
Toe pain band-aids!
Put one on and see if it helps.
If it does...maybe it is in his head, and the band-aid "cured" it.
Maybe he just wants some extra attention.