Southern Speed will not defend her Caulfield Cup title but instead be saved for the Cox Plate the following week.

Barrier 14, the same gate she had when she put in a career-worst effort in the Turnbull Stakes when she beat just one runner home, was a major factor in the decision to withdraw the mare from Saturday's race.

"The barrier was a major concern," trainer Leon Macdonald said.

"She would have had to be as good as Rising Fast to win it and she would have had to carry the most weight for a (winning) mare for 20 years.

"She will be scratched in the morning and we'll wait for the Cox Plate."

Rising Fast won back-to-back Caulfield Cups in 1954/55 while Mannerism in 1992 carried 54.5kg to win, the same weight Southern Speed had in the Cup.

Her withdrawal moves English stayer Gatewood, the second emergency, closer to a start with a decision on Americain's participation to be made on Saturday morning.

Although she won't be at Caulfield, Macdonald says the mare is going as well as last year and will be spot-on for the Cox Plate at Moonee Valley.