A win during the Warrnambool May carnival and subsequent endorsement from a champion jockey has been the catalyst for South Australian trainer John Macmillan to test Arkham Knight in Melbourne for the first time.

Arkham Knight, winner of six of his 19 starts, is set to contest Saturday's $100,000 Brian Beattie Handicap (1400m) at Flemington, a heat of the Winter Championship.

"When Craig Williams won on him at Warrnambool he suggested I pick a couple of those heats of the Winter Championship," Macmillan said.

"He said to me at the time that he's not sure with his other commitments if he would be able to ride him but he felt during winter he was a Saturday-class horse in Melbourne."

Williams will not be riding Arkham Knight on Saturday, with Melbourne's reigning premier jockey to continue his association with Godolphin's Group Two winner Morton's Fork.

"But that doesn't mean the horse isn't worth a roll of the dice anyway," Macmillan said.

Stephen Baster takes the ride on Arkham Knight who has raced twice since that day at Warrnambool on May 3.

He failed in the Group Three R A Lee Stakes (1600m) in Adelaide on May 19 which prompted Macmillan to keep the gelding in South Australia for another start.

He bounced back when he dead-heated for first in a 1250m benchmark race on the Morphettville Parks track on June 9, which confirmed Melbourne plans.

"I think it was that he simply just didn't get the mile in the R A Lee Stakes, but to be certain of it I wanted to run him in one more race in Adelaide before bringing him across to Melbourne," he said.

"He ran in that 1250-metre race, dead-heated for first and in one more stride he would have won (outright).

"That was enough for me to say the horse was on top of his game and we might as well come across and have a try."

Arkham Knight was at $18 on Thursday, with Ozi Choice the $2.40 favourite ahead of Morton's Fork ($7).

Macmillan indicated because Arkham Knight had failed twice over 1600m, he was unlikely to progress to the Listed Winter Championship Final in a couple of weeks.

But the $100,000 stakes was still enough of an incentive to target Saturday's heat of the series.