Sold by Andrew Clayton-Payne of Mayfair to the Rienzi Collection at the Museum of Fine Arts, Houston, the work on paper, 16 x 10 ½ in (40 x 27cm), was priced at £18,000.
The top half of the sheet shows a mythological seduction scene, while below is a sketch of putti playing.
It was among 34 recently rediscovered drawings, more than a third of which sold, offered by the gallery during LAW (June 27-July 5).
They had been bought as an album in a Scandinavian auction.
The group was assembled by Zoffany for his patron Claude Martin (1735-1800).
Until the reappearance of this collection, fewer than 30 Zoffany drawings were known, most already held by institutions.
Nearly 50 galleries took part in LAW, which coincided with the major auctions and other art events taking place around Mayfair and St James’s.
One of the other shows was a joint porcelain exhibition A Collectors’ Paradise held at The Brian Haughton Gallery, also hosting Robyn Robb and Christophe Perlés.
Among the highlights here was a rare Chelsea red anchor mark mug, c.1752-55, painted with a great snow owl, which Robb sold for a price in the region of £10,000.