It might not have seemed a smart move, but trainer David Hayes was in no doubt that asking Zac Purton to ride Criterion in a track gallop was the right call.

A last-start winner of the Queen Elizabeth Stakes during The Championships at Randwick, Criterion is in Hong Kong where he will fly the flag for Australia in Sunday's Audemars Piguet QE 11 Cup at Sha Tin.

Australian Craig Williams has the Group One ride but won't arrive in Hong Kong until the morning of the race.

In his absence, Hayes called on Purton to put Criterion through his paces in a workout at Sha Tin on Wednesday, despite the fact Purton will ride rival runner Military Attack in the feature.

"It's like sleeping with the enemy," Hayes said.

"I'm really happy with him. He's done so well here. Like me, he obviously likes Hong Kong and I was happy and thankful to have Zac (Purton) help us out this morning.

"I didn't want the horse to do too much and I knew Zac would get it right which he did."

Formerly prepared by David Payne in Sydney, Criterion was placed in the Hong Kong Cup in December at his first run for Hayes before returning to Australia for an autumn carnival campaign highlighted by his Queen Elizabeth win.

Hayes believes he has the horse better prepared for an overseas raid this time around.

"I know him now. I've been training him for six months and he's better prepared for Hong Kong this time," Hayes said.

"December was a bit of an afterthought, he'd had hard runs in the Cox Plate and the Mackinnon and he still nearly beat the locals."

Purton gave Hayes a positive assessment of Criterion after the track gallop and said the horse was relaxed and professional.