Premier Sydney trainer Chris Waller will front stewards on Thursday over a positive swab returned by his stayer Junoob after its win in the Group 1 The Metropolitan Stakes at Randwick in October.
The 6-year-old gelding tested positive to Frusemide (an ingredient in Lasix), which is administered to horses to reduce the chances of a bleeding attack.
Stewards received confirmation the B sample was also positive on Wednesday afternoon, with Waller scheduled to front a hearing at 3pm on Thursday.
Trainers can be fined, suspended or even disqualified if they are found to have presented a horse to race with a prohibited substance in its system.
Frusemide is a commonly used anti-bleeding drug, but it is illegal for a horse to have in its system on race day.
Veteran trainer Clarry Connors is also due to front stewards on Thursday, after the John Singleton owned This Is Australia tested positive to Lignocaine following its win on debut at Canterbury in September.