Sheldon left the agency in order to take up a partnership with corporate design firm Lunn Dyer.
His departure reignites rumours of a merger of Australian Bcom3 agencies Burnett and D'Arcy, which comes as French-based Publicis Groupe awaits a decision on its proposed A$5.3 billion (US$3.05 billion) takeover of the Bcom3 network.
Industry sources said a merger is a likely option, given the upheaval D'Arcy is facing following its loss of the global Mars business.
However, Sheldon, who was with Leo Burnett five years, stressed the proposed Publicis takeover and his departure were unrelated.
After collaborating with Lunn Dyer for eight years Sheldon said he was keen to pursue corporate branding more intently and so joined Lunn Dyer as strategic partner.
