Caulfield Cup defending champion Southern Speed is in better form than at this time last year according to trainer Leon Macdonald, but a final decision on whether she runs will not be made until Friday.

Barrier 14 could be the stumbling block to Southern Speed becoming the first mare to win the race in successive years.

"There is a slight doubt and I've left it to the owners," Macdonald said on Thursday.

"As far as I'm concerned there is no reason not to run her but they want to consider everything - how the race will be run and where she will be from the barrier.

"They just want her to be in the race that suits her best and give her the best chance to win.

"The Cox Plate is there if she doesn't run at Caulfield."

There are no issues with Southern Speed and Macdonald is delighted with her build-up despite her shock flop in the Group One Turnbull Stakes (2000m) at Flemington earlier this month.

Southern Speed, who also drew the less than ideal barrier 14 in the Turnbull, was a major letdown when she beat only one runner home.

But Macdonald said he had been highly impressed with her fourth at her previous start in the Group One Underwood Stakes (1800m) at Caulfield.

"Except for the Turnbull Stakes I thought she was going better this year than she was ever going in her lead-up," Macdonald said on Thursday.

"Her run in the Underwood was enormous.

"There was a bit of a glitch in the Turnbull Stakes, I'll admit that.

"She did travel very wide and she probably didn't finish off as well as we would have liked.

"But she's been fine since then."

Macdonald said Southern Speed had also produced an ordinary performance in the Turnbull Stakes last year but it had obviously had no affect on her Caulfield Cup run.

He said the mare could go back-to-back this year but would have to overcome several key factors.

"She can. It's probably a little bit tougher than it was last year.

"She had a perfect barrier draw last year (3). But having said that a lot of the fancied horses are drawn out wide," he said.

While Southern Speed is not cemented in the Caulfield Cup field, neither is Americain, the 2010 Melbourne Cup winner.

If the track is too hard, connections of the stayer say they could also consider the Cox Plate as an option.

Trainer Alain de Royer-Dupre's representative, Stephanie Nigge, will walk the surface with race jockey Gerald Mosse before the horse's place in the field is confirmed.

Ibicenco, the Caulfield Cup third emergency, has been ruled out with a veterinary issue in an another blow for the Luca Cumani stable which was forced on Wednesday to abandon Cox Plate plans for Afsare who suffered a leg injury.