The integrity of the Melbourne Cup is now being questioned after champion jockey Damien Oliver reportedly confessed guilty to allegations that he placed an A$10,000 bet on a rival horse two years ago.

Officials of Racing Victoria remained mum on the issue as it claimed the investigation into Mr Oliver is still ongoing. As such, the top jockey still gets to ride Melbourne Cup's favourite, French-trained Americain.

Americain's owner, millionaire Gerry Ryan, said he still believed in Mr Oliver's capacity to lead his horse to the overall top spot in the finish line. But Mr Oliver actually was a replacement to Gerald Mosse, whom Mr Ryan dismissed when Americain finished a dismal fourth in the Caulfield Cup.

Mr Ryan said he remained confident the controversy-embroiled horse jockey would be focused on his job Tuesday at the Melbourne Cup.

"Damien did call us and explained to both (fellow owner) Kevin Bamford and I that this was going to come up," Mr Ryan told the Seven Network.

Trainer Wayne Hawkes, who was interviewed by ABC News, likewise said Mr Oliver still ought to ride out today since authorities have yet to hand down the verdict and slap him with a guilty pronouncement.

"So I mean if someone hasn't been proven guilty, the Aussie way is innocent until proven guilty so let the stewards decide his fate and go from that," the trainer, who has two horses in the race, named MaLucky Day and Niwot, said.

Reports by Fairfax Media said Mr Oliver had admitted to an investigation body last month that he broke racing rules when he bet on rival horse Miss Octopussy, which won a race in 2010 at Melbourne's Moonee Valley. Mr Oliver, who vied in the same race, finished sixth.

The investigation, according to Racing Victoria Chief Executive Rob Hines, is expected to be completed next week. He called on government to provide racing stewards more power to stand down jockeys suspected of wrongdoing.

"Racing Victoria would welcome a wider stand-down power for the stewards or police that could be used when there is information to support the need to avert a serious risk to the integrity of racing," Mr Hines said.

If Americain wins Tuesday's Melbourne Cup, Mr Oliver gets to pocket hundreds of thousands of dollars, following his ride on Saturday's Victoria Derby winner, Fiveandahalfstar, which earned him A$45,000.