"He has made a number of payments over a number of years that have not been passed by the committee of the Riverton club," Andre Klein, the chief executive officer of Gallop South said.
"He has resigned and there is enough evidence for a police investigation."
"Doug authorised a series of advertisements in a number of publications that fell outside the policies and processes considered satisfactory by Gallop South and its member clubs," Mr Klein said.
"Doug was of the opinion that he was doing something of benefit. However, in hindsight, he has acknowledged this was a gross error of judgement."
Mr Klein said there was no suggestion of personal gain.
Mr Stuart confirmed that the matter was in the hands of the police.
"It is in the hands of the police, simply to verify that I didn't do this for personal gain. The advertisements were to promote the club," Mr Stuart, an administrator for 24 years, said.
