Three-time Grand Annual Steeplechase-winning jockey Steven Pateman is out of the main feature races after he was injured and transferred to hospital.
Pateman was leading race three, a 3200-metre hurdle, at Warrnambool on Tuesday before a fall at the last hurdle.
He suffered concussion and was ruled out of all three feature races at the revamped, crowd-less May carnival.
Pateman's horse in race three, Sir Isaac Newton, was euthanised following the fall.
Racing Victoria said the incident was referred to the Jumps Review Panel.
"It is with sadness that Racing Victoria confirms that Sir Isaac Newton was euthanised by the on-course veterinary staff after sustaining an injury when falling in the maiden hurdle at Warrnambool today," it read.
"His rider, Steven Pateman, sustained a concussion and has been taken to hospital for observation.
"He has been replaced on his remaining rides at today's meeting.
"The racing incident has been referred to the Jumps Review Panel to consider the circumstances and any potential safety enhancements.
"In addition, a post-mortem will be performed on Sir Isaac Newton at the University of Melbourne Veterinary Clinic as is standard practice.
"RV extends it condolences to the owners of Sir Isaac Newton, his trainers Ciaron Maher and David Eustace and the stable staff who cared for the horse."
Pateman was booked on Zed Em in the Grand Annual, Euroman in the Brierly Steeplechase and Mr One Eleven in the Galleywood Hurdle.
Tom Sadler has replaced Pateman on Riding High in a novice hurdle and Aaron Lynch will ride Zed Em in the Grand Annual.
Preusker said his main goal for Inayforhay was exposure to quality racing.
"He got a good experience, that's what we went out to do," he said. "He dug in, it was good to see.
"I think he's the right horse for the bigger fences. He's a nice, relaxed animal.
"He'll keep chipping away through the season."
Preusker praised jockey Lee Horner for his patient ride on Inayforhay, weaving through the field after starting his run at the 700m mark.