Chris Waller won't be a casual observer at Churchill Downs this weekend for the Kentucky Derby. It's not his style.

Sydney's premier trainer flew to the United States on Wednesday for what could best be described as a working holiday, or in racing manager Charlie Duckworth's view - a fact-finding mission.

Although Waller could warrant a spell after a hectic autumn dominated by Winx's all-conquering exploits, he will be having a brainstorming session with Bob Baffert, trainer of the world's best horse, Arrogate.

"Chris is not very casual," Duckworth said.

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"He'll be linking up with Bob and no doubt picking his mind on how we can improve things and do things differently."

Waller and Baffert - a four-time Kentucky Derby winner - met at the Longines Horse of the Year awards in London in January when the American took home the supreme award and Winx was judged the world's best horse of turf.

"It's very similar to when he went to visit Aidan O'Brien at Ballydoyle (Ireland) ," Duckworth said.

"Chris changed and tweaked a few things around."

Baffert, 64, the trainer of four Kentucky Derby winners including 2015 triple crown winner American Pharoah, does not have a runner this year.

Duckworth said there were obvious barriers to Waller one day targeting a race like the Kentucky Derby. "The breeding makes it harder for us," he said. "We'd have to send a two-year-old to run in the Northern Hemisphere against their three-year-olds.

"It's also on a dirt track and that makes it harder because there's no dirt tracks in Australia.

"Having said that I'm scared to rule out too many things with him."

Godolphin has been trying to win the Kentucky Derby since 1999, and Thunder Snow is Sheikh Mohammed's strongest chance yet, trainer Saeed bin Suroor says.

Saeed has sent seven of nine Godolphin contenders to the Derby but says he has "been waiting for this moment for a long time".

"Thunder Snow is a tough horse with a lot of class, which you need because the Kentucky Derby is a very, very tough race," he said.

"He's the best horse we have ever sent [to the Derby]."

•Thunder Snow has drawn barrier two for tomorrow's race meaning that jockey Christophe Soumillon will need to go forward from the start.

Almost a week after reports surfaced John O'Shea had resigned as its head Australian trainer, Godolphin last night confirmed he has stepped down.

Darren Beadman, right hand man to O'Shea during his three-year tenure, was granted a trainer's licence yesterday with horses to race under his name from tomorrow.

- AAP