Failure to acquaint themselves with the racing rules has cost trainer Trent Busuttin and his vet Dr David Garth $2000 each.

More significantly it also cost New Zealand colt El Roca the chance to run in Saturday's Hobartville Stakes, a vital lead-up to the Group One Randwick Guineas in two weeks.

Racing NSW stewards withdrew the pre-race favourite after being notified of a breach of the rules regarding pre-race treatment.

Chief investigator Nathan Hayward reported a mark on El Roca's neck which treatment records showed had been caused by the intravenous administration of an alkalinising agent at 6am on Friday.

The rules state treatment cannot be given within a clear day of a horse racing, in this case midnight Thursday.

In Victoria, where Garth is originally from, the local rule is different, starting a 24-hour period before a race.

Blood tests confirmed El Roca had a TCO2 level lower than the allowable limit but Murrihy said his panel had decided it was unfair to the other runners to let El Roca start.

"There was no intent, just ignorance," Busuttin said.

"We have paid dearly and the owners have paid dearly."

Garth admitted he should have familiarised himself with the rule, having been in NSW for two months.

"It was an oversight on my part," he said.

Both were fined $2000 and stewards gave Busuttin the option to trial El Roca on Tuesday but the trainer said his preference would be to run in the Liverpool City Cup at Warwick Farm next Saturday.

Murrihy said he would also investigate why Victoria was operating under a local rule from March last year when a new Australian rule had been introduced in September.