SGL, from France, sells on 24 June 2018 a "Flemish School, ca. 1600" Hercules and the snakes, estimated at 3,000 to 5,000 Euro.
Christie's in 2015 for £11,800, but the two works are different enough to suppose that some engraving was the basis for it.
Rijksmuseum site I found this anonymous engraving, from a 1584 Italian book on ancient Roman sculptures.
RKD showed me the actual sculpture, currently in the Uffizi.
Whether the artist of the work for sale knew the engraving (or another one of the same work), or had seen the original sculpture, is hard to know of course.