Chris Waller will front a stewards' inquiry on Friday after three horses from his premiership-winning racing stable returned positive swabs.
A Racing NSW statement on Thursday confirmed the presence of Ibuprofen, a non-steroidal anti-inflammatory, in four swabs belonging to three horses.
Among the horses to test positive is the in-form Arinosa, a mare who has been one of the revelations of the Sydney carnival with three autumn wins.
Arinosa's swab relates to her first-up success in the Listed Wenona Girl Quality at Warwick Farm last month.
The five-year-old has since won the Birthday Card Stakes at Group Three level and Group Two Sapphire Stakes.
Stewards have confirmed they took samples of the feed used at Waller's stables last month with 11 containers sent to the Australian Racing Forensic Laboratory for analysis.
Non-raceday samples from seven Waller-trained horses have also been analysed.
"Basically we got advised we got an irregularity and unfortunately it appears to have come from feed contamination but it's up to the stewards to determine that tomorrow," Waller told AAP.
"(The stewards) have been very co-operative as we have. Once we were aware of the problem we didn't race any horses and they've since been cleared to race."
Waller said the outbreak of positives had been confined to a small part of his Rosehill training stables.
"It was one barn of six horses and as soon as we were aware of the problem we stopped them from racing until they were clear," Waller said.
"It's an over-the-counter medicine which they have tested to. We worked out we make about 140,000 feeds a year.
"When we had one (irregularity) we had no idea where it had come from, but as soon as we had two we started to put things together."
Waller is on target for a record-breaking season as he chases his third Sydney premiership.
Before Thursday's Anzac Day meeting at Warwick Farm, he had trained 126-1/2 winners in 2012-2013 to put himself well within reach of the Sydney record of 156 winners shared by Tommy Smith and his daughter Gai Waterhouse.
He celebrated a Group One double at Randwick last Saturday when Royal Descent blitzed her rivals in the Australian Oaks and Sacred Falls came from last to give him a third Doncaster Mile triumph.
Waller will be strongly favoured to add to his Group One haul at Randwick on Saturday when he saddles up favourite Kelinni in the Sydney Cup.