The half-brother of Australia's unbeaten champion race horse Black Caviar is battling for his life after being bitten by a venomous spider. Bought for Aus$5 million (€3.5 million) in April, Australia's most expensive yearling is being treated at an equine clinic outside Melbourne.

"His life is on the line, he's a 50-50 prospect and we hold grave concerns for him," equine vet Tom Brennan told Australian news agency AAP. Named Jimmy, the colt suffered an adverse reaction to antibiotics, which led to an onset of the hoof disease laminitis in his two front feet, Brennan said.

The next couple of days would be crucial for the horse, Brennan added.

“We’re hopeful, if he has no further complications, there is still a slim chance we may be able to get him to the racetrack but, at the moment, we’re focused on trying to save him and his breeding career.”

Jimmy was brought to the equine clinic two weeks ago after the suspected bite from a white-tailed spider.

"We invest our lives in horses and to have him as a member of our team was a dream," Simon Marshall, a spokesman for the syndicate which bought the colt, said. "We were really looking forward to a bright future," he added.

Sprinter Black Caviar went 25 races unbeaten before retiring in April.