Hyett, who has already been interviewed by Racing Victoria stewards, is expected to be called again to give evidence in the next few weeks.

A registered stablehand employed by Aquanita Racing at the time, she was not permitted under the rules to lay horses from her stable to lose.

Investigations  began when almost $260,000 was held on an Echuca race on March 8, the bets centred around Baron Archer to lose.

Fairfax Media understands Hyett left the stable after her position became redundant before the inquiry.

A spokesperson for Aquanita Racing said last night that a board member of the business had been interviewed by Racing Victoria integrity officers.

It is believed that stewards also found other bets on Aquanita horses to lose on Hyett's account.

"It's very concerning as we've worked hard to create a strong brand name in racing but local, interstate and overseas clients have all been briefed on the matter," the spokesman said on Tuesday night, adding that Hyett had been   highly thought of by Aquanita.

Stewards have been concerned for some time over a number of wagers that caused her account to spike on certain days.    Nikolic has lived with Hyett for several years.

Stewards said they had no problems with Ben Melham's ride on Baron Archer at Echuca but have taken issue with the horse's trainer, Jason Warren.

Warren did not advise stewards that the horse had undergone a throat operation before returning to racing.

The investigation will continue on  Friday of next week. The sophisticated betting monitoring system based at Flemington can identify any significant market moves, which  are sent trackside where stewards can question those involved.

Nikolic, 40, has said he is keen to return to riding.