Margie: Is this an indoor house plant or an outdoor species in your garden? I can't tell if I see a pot in the photo. If it's a potted fig, the problem could be overwatering, poor drainage or root bound. You might try repotting in a larger pot and/or watering less. But figs are susceptible to a variety of pests including fungal diseases, spider mites, and other parasites.

If it's not overwatering or poor drainage, based on the photo you sent, the single brown spot looks most typical of anthracnose fungus. It is caused by the Colletrotrichum gloeosporioides fungus and typically appears during warm, humid weather. Our summer has been hotter than usual and humid as usual! Anthracnose can damage your fig tree’s leaves, fruit, and stems. 

Another fungal disease that can cause brown spots on fig tree leaves is fig rust. The first signs of fig rust on fruit trees are tiny yellow spots on the underside of leaves. The rust on fig leaves’ underside then spreads to the upper portion, and the spots become reddish-brown. But your photo doesn't look like a rust.

To treat a fungus, cut away the affected leaves, branches and other infected parts. Since anthracnose fungus is found in the soil, you'll should discard the leaves in the trash. There are several options for treatment, neem oil spray can work on some infestation, a copper-based or potassium bicarbonate-based fungicide will work to kill the fungus in potting soil and on the plant. Any of these products are available at a nursery or garden supply store.

Good luck treating your fig.

Regards,

You're welcome!