Chris Waller senses Grand Marshal is running on empty ahead of The BMW, and fears Rosehill's next headline Group One race will be the English import's swan song.

The seven-year-old gelding, who started his career in a two-year-old maiden at Salisbury in 2012, began his Australian career with Waller's stable two years later and since then has racked up the mileage and taken his prize money to a tick over $2 million.

Grand Marshal's success in the Moonee Valley Gold Cup in October has been the one bright spot this season and the BMW's $71 outsider in the nine-horse field is liable to pound through a heavy track for the last time on Saturday.

"He's going poorly. He needs to turn his form around. He needs to do something on Saturday to continue racing, he's got to pull his finger out" Waller said, before issuing a partial retraction.

"It's a bit detrimental to say 'he's got to pull his finger out'. He might be saying the same thing like 'Chris I've changed, you need to try and do a few different things'."

Waller took that hypothetical message on board in the lead-up to Grand Marshal's 41st start, mixing up the preparation by running him over a couple of fences this week with fellow veteran and starter in the $1.5 million 2400m feature, Who Shot Thebarman.

"Grand Marshal's been a good horse. He's a Sydney Cup winner (2015), he was third the Sydney Cup last year. He's run in a couple of Melbourne Cups (2015-16), it takes its toll.

"He's lost a bit of desire. He's done a lot of miles."

Grand Marshal returned from a 17-week spell in January but made no impression in three barrier trials before running ninth of 10 and then last in the Chipping Norton Stakes and Sky High Stakes respectively.

"Like all of us, we can only compete at our best for so long and he's just starting to drop off, that last preparation included when he did happen to win a Moonee Valley Gold Cup," Waller said.

He was more upbeat about Who Shot Thebarman ($17), describing the eight-year-old as "going terrific" before he hits a heavy 10 track and a quality field including Jameka who was the TAB's $3.80 favourite on Thursday.

"He'll like the conditions and the prospect of a tough staying race. It'll be a gut buster. He's that old sort of warhorse that can turn up," Waller said.

Waller also has six-year-old gelding Libran ($26) finally tackling his preferred distance.

"There's a sense of timing about him," he said.

"He ran second in the Sydney Cup last year, he had a good (44-week) spell, he's had three runs back and gets to the right distance on Saturday.

"The BMW and the Sydney Cup are the races he's been set for."