This small panel with the figure of David in an emotive and exaggerated pose relates closely to the work of Cerano in the early years of the 17th Century.  It is reminiscent of a number of paintings, most particularly the Saint George and the Dragon in the Brera, Milan, dateable to 1605-10 (inv. 389, see M. Rosci, Cerano, Milan, 2000, cat. no. 75).  The Brera picture is also on panel and of small format, but painted in a looser style, perhaps as a bozzetto rather than a finished work.  Interestingly, that picture entered the museum's collection attributed to Morazzone, to whom the present panel has been attributed to in the past (based on old labels on the reverse).