Darren Weir has decided to back Stratum Star up in the Group Three David Jones Cup at Caulfield as the Group One winner continues on a path to the Mackinnon Stakes.

Stratum Star won the Sir Rupert Clarke Stakes (1400m) earlier this spring and has been placed in two other Group One races this campaign - the Memsie Stakes and last Saturday's Toorak Handicap.

Weir has another Group One target in his sights with Stratum Star in the Mackinnon Stakes (2000m) on October 31 at Flemington but felt three weeks the Toorak (1600m) and the Mackinnon was too long.

He decided to back the four-year-old entire up in Saturday's David Jones Cup (2000m) with Mark Zahra to replace Craig Williams who already had another ride not expecting Stratum Star to run.

Stratum Star has topweight of 59kg and is the early favourite at $3.20 ahead of Sadler's Lake ($4) and Fenway ($4.60).

"The plan is the Mackinnon and I felt because he's such a casual trackworker, he might just get away on us if we go three weeks into the Mackinnon," Weir said.

Stratum Star has only raced over further than 1600m once in his career when beaten a short half-head in the Alister Clark Stakes (2040m) at Moonee Valley as an autumn three-year-old.

"He ran well in the race at Moonee Valley (over 2040m)," Weir said.

"I think 2000 is what he's looking for."