Believe it or not, if your wife has some Canesten Cream lying around in the medicine cabinet, that will do the trick. Preferably the 2% strength thrush cream (clotrimazole). Pop that on two times a day, or even three if you've got nothing better to do

onto the foot, cleaned and dry.
and it'll clear up pretty soon. Nip it in the bud before it spreads and starts to get really flakey and odorous. Other tips are to keep the offending foot dry, let it air if you can and wear cotton socks for a few days, preferably with porous footwear to allow the skin to breathe.
There's loads of stuff on the market. Mycil is a good old brand that has been around for ages. Daktarin and Scholl also make sprays, creams and powders for Athlete's foot. Lamisil Once (RRP £8.99) is the creme de la creme of treatments blasting away the offending fungal infection (tinea pedis) with a one off treatment that involves coating both feet.