As Belle Couture moves closer to a race debut, her younger brother has made "slight improvement" in a Victorian veterinary clinic as he battles the hoof disease laminitis.

Three-year-old filly Belle Couture and the unnamed two-year-old colt, known as Jimmy, are both half siblings to champion mare Black Caviar and also multiple Group One winner All Too Hard.

Belle Couture and `Jimmy' were bought as yearlings by BC3 Thoroughbreds, with the colt fetching a record price for a yearling at public auction in Australia when knocked down for $5 million at this year's Easter Sale.

BC3 spokesman Simon Marshall was at Flemington on Friday to watch Belle Couture win a jump-out, and he also gave an update on `Jimmy' who developed laminitis last month.

The colt was bitten by a white tail spider and developed the life-threatening hoof disease after suffering an adverse reaction to antibiotics.

"Jimmy is really well for the environment that he is in," Marshall said.

"There's slight improvement, but not much. He's not out of the woods.

"They are really happy with where he is heading, to be honest, so it has given us a slight bit of positivity but with laminitis it can flare up at any stage.

"His feet are stabilised which is the most important thing for him. But he's not out of the woods."

The Danny O'Brien-trained Belle Couture, meanwhile, is likely to make her debut this month.