Spieth's on-again, off-again Caulfield Guineas campaign can take another twist on Saturday.

The lightly raced Spieth lines up in the Group Three Caulfield Guineas Prelude (1400m) in a race that will decide if he continues to step up in distance or comes back to sprinting.

An original entry for the Caulfield Guineas (1600m) on October 10, Spieth was missing from the latest list and a $55,000 fee will need to be paid to run in the race.

However, Spieth is a nomination for the Listed Blue Sapphire Stakes (1200m) on the middle day of the Caulfield Cup carnival.

"He's not paid up for the Guineas, but that's only because we were running out of time," trainer Bryce Heys said.

"It's up to him to put the writing on the wall to justify heading towards the Guineas.

"The Guineas Prelude is a step up, let alone thinking about going to a Guineas.

"At the same time he's going to run very well but I've got no hesitation in keeping him for a short-course either post Saturday."

Spieth will be having his third outing on Saturday.

He was an unlucky second behind quality filly Secret Agenda before scoring a comfortable win in maiden grade at Pakenham on September 16.

Heys said the plan was to always head to Pakenham before tackling the 1400m of the Guineas Prelude.

"There were two races he could go into after his debut and providing his performance at Pakenham second-up was adequate it would lay a good foundation to try him at 1400 metres at Caulfield," Heys said.

The draw of 13 in the 16-horse field is not ideal but Heys said it was better than drawing barrier one.

Heys said the son of Thorn Park was still learning about racing as he looks forward to seeing the colt race over 1400m.