Classy filly Shoals puts her unbeaten run on the line at Caulfield in a race that will be telling for her Thousand Guineas prospects.

Shoals is aiming for her fifth-straight win when she lines up in the Group Two Thousand Guineas Prelude on Sunday, her second start this spring and her first try over 1400m.

The filly is yet to race beyond 1200m and trainer Anthony Freedman is still unsure whether the three-year-old will be effective at 1600m, the distance of the Group One Thousand Guineas on October 14.

"I'm not convinced but Sunday will tell," Freedman said.

"She needs to finish it right off and put her hand up for the mile."

Blue Diamond Stakes winner Catchy is the ruling $2 favourite.

Booker, second in both the McNeil Stakes and Danehill Stakes this spring, is at $5 with Shoals at $7.

Shoals won the Listed Atlantic Jewel Stakes (1200m) first-up this campaign at Moonee Valley to add to her juvenile wins in the Group Three Thoroughbred Breeders Stakes and Group Two Percy Sykes Stakes.

She has the outside barrier in Sunday's field of nine for what shapes as a campaign-defining race.

"She's drawn a bit tricky so we have to have a look at how we ride her," Freedman said.

"But she's in good order. I'm happy with her. She's fit and well."

Catchy is the $3.60 favourite for the Thousand Guineas but could instead take on the colts and geldings in the richer Caulfield Guineas on the same day.