Progressive four-year-old Von Tunzelman will be taking a step into the unknown at Ellerslie on Thursday.

The son of Zabeel faces the toughest test of his brief career when he makes his Group One debut in the Bonecrusher New Zealand Stakes.

"He's not well off at weight-for-age and is still a bit green and immature, but he's an up and comer and a fit horse," his rider Leith Innes said.

Trained by Roger James for breeder-owners Brendan and Jo Lindsay, Von Tunzelman has won four of his 10 starts with the latest of them a Listed defeat of the Group One winner Fanatic in the Kaimai Stakes at Matamata.

Innes acknowledged the significant step up in class facing Von Tunzelman and he said it was only a matter of time before the four-year-old made his mark at the top level.

"Regardless of what he does this week, he should be knocking on the door in these sorts of races next year."

Innes speaks from experience with 27 Group One victories to his credit and he has high hopes of also adding a first Barfoot & Thompson Auckland Cup to his CV when he combines with Chenille.

"She definitely looks to be one of my best chances," he said. "She's well weighted and I'm sure she will run well if the track improves to a firmer surface."

Innes has trimmed down to partner Chenille at 53.5kg.

"That's about as light as I ride, but it's worth making the effort," he said.

"You don't get many chances to win an Auckland Cup and it's a race I want to win. I don't think two miles is going to be a problem for her."