We are grateful to Mercedes Royo Villanova for confirming the attribution from a transparency. She points out the strong resemblances between Saint Jerome in the present picture and the figure of Saint Joseph in De Clerck's Lineage of Saint Anne of 1590, in the Musées Royaux des Beaux-Arts in Brussels, and the old man in his Susannah and the Elders in the Rijksmuseum, Amsterdam (no. 696).
Hendrick de Clerck was native to Brussels, where he was made court painter to Archduke Albert and Archduchess Isabella in 1606, but he probably studied in Antwerp, under Marten de Vos (1532-1603). Certainly the influence of the Antwerp School, which permeates his oeuvre, is clear in the present picture. The sharply-defined contours and powerful naturalistic detail seem to recall earlier depictions of the saint by Jan van Hemessen (c. 1500-c. 1566; see M.J. Friedländer, Early Netherlandish Painting, XII, Leyden and Brussels, 1975, pls. 114-5).
The present composition also seems to be echoed in Rubens's pictures of the same subject at Sanssoucis, Potsdam, and the Staatliche Kunstsammlungen, Dresden, (M. Jaffé, Rubens, Milan, 1989, p. 164, no. 84 and p. 207, no. 311); the Potsdam painting also depicts a similarly wide-eyed, benign-looking lion.