Allen will now partner fancied Irish raider Thomas Hobson after Moreira plunged to the turf in a heavy fall from his mount Regal Monarch in the Ronald McDonald Charities House Plate, one of the support races earlier on Cup Day.

The Asian-based rider, known as "Magic Man" for his phenomenal success in Hong Kong and before that Singapore, crashed to the ground after the former English stayer fell at the top of the straight..

Replays suggested the horse went amiss and may have clipped the heels of a rival just in front as the field headed into the closing stages of the race. Moreira tried to pull the horse up as it veered across the track, but it continued for a couple of strides before crashing to the ground.

Moreira fell heavily and bounced along the turf before rolling clear. No following horses were brought down.

The jockey subsequently got to his feet and walked to a waiting ambulance.

The horse has been taken to Werribee Vet Clinic for treatment. He is owned in the same interests as stablemate Libran, which will contest the Melbourne Cup.

Mullins, one of Ireland's leading jumps trainers, almost took the race two years ago when Max Dynamite, one of his representatives in this year's Cup, ran second.

He believes Thomas Hobson is a live chance, but was disappointed at the turn of events.

"It is [disappointing for Joao Moreira] and it's disappointing for us too I'm afraid. It's more like something that happens in jumps racing

"Everyone has been a great help to me. The minute this thing happened we started searching and came up with two or three names and Ben was the name everyone came up with.

"I'm happy with that, I've spoken to him and he's looking forward to it. He has watched a few of the horse's races, he knew about the horse so it makes it easier

"He's an up and coming rider, the fact he is young (worked in his favour) I felt I wanted to go that way."

Allen has been one of Victoria's leading apprentices for the past couple of seasons, riding many winners for the all-powerful Darren Weir stable.

He went close earlier this spring in the Caulfield Cup, finishing fourth on another former English trained galloper Lord Fandango.