Trainer John McArdle has suffered a blow with boom colt Doubt I'm Dreaming collapsing and dying at trackwork.

The Mornington trainer rated Doubt I'm Dreaming potentially the best horse he has trained, with the colt a dominant winner of a Listed race at Moonee Valley on debut before being beaten at his second start at Caulfield.

After his debut win in December, Newgate Farm and the China Horse Club bought into the colt and he was considered a Caulfield Guineas contender.

"I think he's the best horse I've trained," McArdle told RSN927.

"Hollow Bullet was a multiple Group One winner, but this horse could do things that even she couldn't."

McArdle said the colt was going through routine trackwork on Tuesday when he collapsed.

"He went out onto the track as he does every day with his normal track rider, Daniel Schmidt," McArdle said.

"He was working around the track, no problems at all. I actually looked away to see if one of my other horses was coming off the trotting ring to have a gallop, and I looked back and he wasn't where he should have been.

"I looked further back down the track and he'd stopped. I thought he must have hurt himself so I ran down there. By the time I got there he had collapsed and died."

McArdle said it was a blow and naturally he, his stable staff and the colt's owners were devastated by the loss.

"All the owners are obviously devastated and my stable staff and myself, it's a big loss for us," he said.

"But to put some perspective on it with the tragedy that happened with the Philpot family at Bendigo, at least all of our staff went home."

Donna Philpot, a former jockey and track rider, died at Bendigo racecourse on Tuesday from injuries sustained in a fall in a jump-out.

Philpot, wife of Bendigo trainer Gus Philpot, was a registered stable employee and trackwork rider.