Anthony Cummings will leave a decision on an Australian Cup start for three-year-old Thunder Fantasy until acceptance time.

Thunder Fantasy finished strongly for third in Saturday's Group One Australian Guineas and is on the third line of betting at $8.50 alongside Foreteller for Saturday's 2000m weight-for-age feature.

Melbourne Cup winner Fiorente is the dominant favourite at $1.90 with star three-year-old Shamus Award, winner of the Cox Plate and the Australian Guineas, at $5.

Cummings said the Australian Cup (2000m) was tempting but in terms of an Australian Derby preparation it could complicate things.

The trainer also has the option of the $3 million Doncaster (1600m) on the same day as the $2 million Australian Derby (2400m) on April 12 to consider.

"The Championships are the main aim. There are two possibilities there. One is the Derby and the other is the Doncaster," Cummings said.

"Running in the Australian Cup makes it much tougher, and almost rules out the Doncaster. He may not run there anyway, but it's still a live option now."

The Group One Rosehill Guineas (2000m) later this month is also on the agenda.

"We've just got to have a think and see how he presents on Wednesday morning which is pay-up day," Cummings said.

The trainer went close to winning last year's Australian Cup with three-year-old Fiveandahalfstar.

He was narrowly beaten by another three-year-old, Super Cool.

Saturday's other Group One at Flemington is the Newmarket Handicap and Cummings has Fontelina set to resume.

Fontelina has won the Group Two Yellowglen Stakes (1200m) over the same course and distance at the past two spring carnivals.

The gelding was fourth in the Group One VRC Sprint at his most recent start last November.

Meanwhile, stewards have been told the Peter Snowden-trained Newmarket-bound Knoydart is being treated with antibiotics after a post-gallop scope on Monday detected low-grade mucus.