The curtain is drawing to a close on the career of grand Godolphin galloper Hartnell who will attempt to add to his Group One record one final time in the Mackinnon Stakes at Flemington.

Saturday's weight-for-age race over 2000m is expected to be the last time Hartnell is seen at Flemington as the Godolphin team contemplate retirement for the stable warrior.

Trainer James Cummings says Hartnell has transcended the usual meaning of what it is to be a racehorse for Godolphin.

Hartnell arrived in Australia in early 2015 after starting his career in the UK with Mark Johnston and immediately put his stamp on Australian racing winning the Group One BMW Stakes at Rosehill at his third start.

It was the first of four Group One wins for Hartnell who clashed with champion Winx throughout his career while also mixing it with the best, not only at weight-for-age, but with big weights in feature handicaps.

In all, Hartnell has started 57 times, won 13 races, eight on Australian soil, with a further 22 minor placings and prize money of almost $7.3 million.

Cummings took over the training of Hartnell from John O'Shea in 2017, winning first-up in the Group Two PB Lawrence Stakes at Caulfield.

It was a win that cost Melbourne Cup winning jockey Craig Williams a $2000 fine after the rider added some farrier's gear to make sure he weighed in correctly.

"For a long period of time he's been the best horse Godolphin has raced in Australia," Cummings said.

"He has an amazing ability to always be figuring in the biggest races.

"It surprises some people that he's only won four Group One races, they think he's won more than that.

"But 10 of his wins have been in stakes races and he was placed in Group Ones 13 times.

"It's an amazing record."

Cummings says the looming retirement of Hartnell would leave a big hole in the stable.

He said staff, both in Melbourne and Sydney, would miss him.

"He means much more than a normal racehorse, he's tapped into something deeper for all of us," Cummings said.

"We count ourselves lucky that he came along in our time at the stable."

Hartnell sits on the third line of betting at $8.50 on Saturday behind star New Zealand mare Melody Belle ($3.80) and Melbourne Cup runner Magic Wand ($6.50).