Spotless Group chief executive Martin Sheppard has quit the cleaning, catering and facilities management company after a rollercoaster 21 months at the helm, as frustrated predator Downer EDI sits at 87.4 per cent ownership in its $1.2 billion bid.

The resignation of Mr Sheppard, who joined Spotless as chief executive in November, 2015 after 23 years at KPMG, comes just two days before the company is scheduled to announce its full-year results on August 24.