Australian Derby winner Riff Rocket is out of the spring carnival after undergoing emergency surgery overnight for colic.

The four-year-old had been due to contest the Makybe Diva Stakes (1600m) at Flemington on Saturday and was a $9 equal second favourite for the Caulfield Cup (2400m).

Trainer Chris Waller reported Riff Rocket was taken to the South Eastern Equine Hospital in Victoria on Tuesday night where he underwent a procedure, with first indications suggesting it had gone well.

However, colic can be fatal in horses and the coming days will be crucial.

“Early signs are promising but the next few days will obviously be very important for his ongoing health and survival, which is our main concern,” Waller said in a statement.

“They found the impaction in his large colon, which has been relieved, so our thanks go out to them, as well as our stable vet and staff who picked up the issue early.”

Riff Rocket last year became just the fourth horse to capture the Victoria Derby (2500m) in the spring and the ATC Australian Derby (2400m) in the autumn, with victories in the C S Hayes Stakes (1400m) and Rosehill Guineas (2000m) sandwiched in between.

There were high hopes for him this spring after he opened his account with an eye-catching effort behind class stablemate Via Sistina in the Winx Stakes (1400m) at Randwick last month.

While he won’t be seen again this year, Waller remains hopeful Riff Rocket can pull through the coming days and get back to the races in 2025.