The Victorian jockey at the centre of allegations he bet against a horse he was riding has been dumped from one of the top chances in Australia's most prestigious race.
Reports in Sunday newspapers say two-time Melbourne Cup winner Damien Oliver is alleged to have placed a $10,000 bet on a horse other than the one he rode.
The reports in Fairfax newspapers say Oliver backed the horse Miss Octopussy through a third party.
Miss Octopussy, the favourite, duly won the race at Moonee Valley in Melbourne in October 2010.
Oliver has denied any wrongdoing, saying in a statement he has always been "honest, committed and trustworthy".
The allegation stems from police inquiries into race fixing that have implicated several jockeys, including the recently disqualified Danny Nikolic, and are being investigated by racing stewards.
Owner Lloyd Williams would not confirm if his decision to replace Oliver on second favourite Green Moon in this month's $3 million Cox Plate had anything to do with the reports.
Inquiries to the prolific owner drew a "no comment".
Victoria's chief racing steward Terry Bailey also declined to comment, saying the matter was the subject of investigation by his team.
The allegations come during a difficult period in Victorian racing, in which figures in the sport have also been questioned in connection with the murder of Sydney man Les Samba.
Mr Samba, who was shot dead in a Melbourne street in February last year, is Nikolic's former father-in-law.
Police have cleared Nikolic of involvement in the killing.
They have linked their investigations into the murder with other allegations of race fixing but have not revealed what the link may be.
While the allegations against Oliver have coincided with his sacking from Green Moon it is unclear if the two events are connected.
Mr Williams announced on Saturday that Oliver would ride the horse, only to announce in an SMS to racing insiders a day later that he was sacked.
At the same time, Oliver's replacement, Craig Williams, who is no relation to the owner, gained a release from the favourite Pierro, which suffered a shock defeat at Caulfield on Saturday.
Williams had previously been Green Moon's regular partner but had preferred to ride Pierro, which until Saturday had been undefeated in his eight starts.
Victorian Premier Ted Baillieu said he could understand any anxious reaction to the allegations against Oliver.
"Obviously there is an inquiry under way and I think that's important," Mr Baillieu told reporters.
"I can understand there would be some anxiousness about this but I'm sure Victorians understand that the Spring Racing Carnival is a pretty special event."
Victorian Opposition Leader Daniel Andrews said Racing Minister Denis Napthine needed to ensure racing integrity was taken seriously and was maintained at a high standard.