American import Winchester might be a well credentialled Cups chance but on a wet track he's about the worst horse trainer John Sadler has seen.

And steady rain is forecast at Flemington on Saturday when the eight-year-old is set to contest the $500,000 Group One Turnbull Stakes (2000m).

Historically a key pointer to the Caulfield Cup, the Turnbull Stakes is also an early indicator of what a stable can expect from a spring campaign.

"You go there and you're probably going to find out where your spring's heading in a race like this," Sadler said on Thursday.

"The winner of the Caulfield Cup, Cox Plate and the Melbourne Cup could be in this race so there's nowhere to hide."

Sadler was pleased with Winchester's first start in 10 months when he finished ninth of 14 in the Group One Underwood Stakes (1800m) at Caulfield two weeks ago.

But that was on a good track and given the rain forecast this Saturday there is a chance the stallion will be scratched.

"A couple of times when we went to give him a hit-out it was on wet ground and he's as bad as I've ever seen a horse on wet ground," Sadler said.

"He just does not go on it at all, so going into the Underwood Stakes the other day I really didn't know what to think.

"You would imagine under normal circumstances that race is going to bring him on a lot so we're pretty excited about him but just hoping for no rain."

Sadler described Winchester's Underwood run as "a huge relief" but he was wary of conditions this weekend.

"If if rains he won't run but the track would have to be worse than dead four," he said.

"He would then probably run in the Caulfield Stakes the following week then back up in the Caulfield Cup."

A four-time Group One winner, Winchester began his racing career in Ireland before heading to the US where he took out the Secretariat Stakes over 2000m by more than seven lengths at his first start there.

The entire has drawn wide in barrier 17 and will be ridden quietly, while Sadler's other Turnbull runner, six-year-old Linton, is expected to go forward from gate eight.

The Turnbull will determine which of the coming major events Linton will be set for - either the Caulfield Cup or the Cox Plate.

"He'd have to run a blinder to run in the Cox Plate, the more realistic race is the Caulfield Cup," Sadler said.