I cannot make a definite diagnosis from a photo alone. The lesion looks most consistent with nummular eczema (coin-shaped dermatitis): a small round, dry, scaly, mildly inflamed patch.

An important alternative is tinea corporis (ringworm), especially if it is enlarging with a more raised, scaly outer edge and relative clearing in the center. Ringworm can closely resemble nummular eczema, as noted by the American Academy of Dermatology. A clinician can confirm fungus with a simple skin scraping/KOH test; classic tinea typically forms an expanding scaly ring with central clearing, per the CDC.