A Cox Plate possibility has crept back into the thinking of trainer Leon Macdonald as he approaches Saturday's spring-defining Group One Turnbull Stakes at Flemington with high-class mare Southern Speed.

And at the other end of the spectrum, the Melbourne Cup looms as another alternative, particularly if Southern Speed's bid for back-to-back Caulfield Cups is unsuccessful.

Southern Speed is on the third line of betting in Turnbull markets that are headed by Green Moon.

Macdonald is hoping for a return to winning form in the Turnbull, but a wide barrier and some hot opposition has him looking as much to how she finishes in the race as to where.

If the run suggests she is becoming more dour, the Melbourne Cup will come into calculations.

If not, it could support a Cox Plate run after the Caulfield Cup.

"She is still in the Cox Plate and we will pay up on Tuesday," Macdonald said.

"But if I don't think she can win then she won't run.

"She is still in the Melbourne Cup and I think she can run 3200 metres, but if she won the Caulfield Cup she would get a penalty and the weight would then be a factor."

The Turnbull barrier draw has also presented its own set of choices for Macdonald and jockey Glen Boss.

"I won't talk to Glen until before the race, I don't want to tie him down," the trainer said.

"It's an awkward draw, half of them will want to go back so maybe she will go forward.

"Ideally she could be three-wide with a bit of cover."

The Turnbull is being approached with a similar philosophy by New Zealand trainer Shaune Ritchie who views the race with a mixture of hope and reality.

Zurella made an impressive Australian debut, winning the Group Two Let's Elope Stakes (1400m) at Flemington four weeks ago, but then flopped over the 2000m of Saturday's race when second-up at Caulfield.

Ritchie said the mare was found to be suffering a respiratory problem after the Caulfield run which he is hoping will explain the performance.

"She had a coughing attack after Caulfield and we had her looked at," Ritchie said.

"It hasn't been an issue since, so I'm very hopeful she'll return to the level she was at in the Let's Elope.

"It's just a matter of whether that's good enough in a field like we've got in the Turnbull."

Green Moon holds Turnbull favouritism at $4.80 ahead of December Draw and $6 and Southern Speed and Voila Ici together at $7.