With the luxury of Quackerjack's place in the Doncaster assured for months, trainer Mark Newnham has been able to tailor his preparation to ensure the timing is perfect heading into the famous Randwick mile.

Quackerjack earned a ballot exemption to Saturday's Group One Doncaster Mile when he won the Group Two Villiers Stakes over the course in December.

The four-year-old has performed at his best off three-week gaps between races, so Newnham has stuck to that model after his last-start fourth in the Ajax Stakes on a heavy track.

"His preparation has gone the way I wanted it," Newnham said.

"His best performances have been when he's had three weeks between runs.

"He was three weeks into the Goulburn Cup which he won. He was three weeks into The Gong which he was narrowly beaten in and he was three weeks into The Villiers which he won.

"With his preparation this time it wasn't suitable to do that between the first and second-up runs so he had two weeks between his first and his second run but he's had three weeks between the Ajax and the Doncaster."

Quackerjack began his campaign with victory in the Liverpool City Cup (1300m) and Newnham believes he profiles well to be a contender in the Doncaster.

He drops to 53.5kg having carried 56.5kg and 58.5kg in his two starts this preparation.

He has drawn barrier one and will be ridden by Rachel King who was aboard in the Villiers.

Josh Parr has ridden Quackerjack in both starts this autumn but his Doncaster weight is below his comfort zone.

Newnham and King combined for their first Group One wins with Maid Of Heaven in the 2018 Spring Champion Stakes at Randwick.

Parr and King share much of the stable's riding duties and the former will be aboard Shadow Hero in Saturday's Australian Derby.

"It's a really strong race, it's probably going to be 6 or 7/1 the field, but he's got the right profile for a Doncaster," Newnham said.

"On pace down in the weights. That generally gives you a big advantage.

"The form out of the race he won first-up has been very good with Vegadaze, Imaging and Cascadian all winning since.

"He's got good Randwick form, good Randwick form over a mile and he's down in the weights. He's looking good."

Quackerjack was at $15 on Wednesday with three-year-old colt Brandenburg the $6 favourite.