Past events ensured jockey Peter Robl tempered his enthusiasm over the improving Golden Slipper fortunes of Assail despite the filly's barrier trial win on Tuesday.

The central figure in one of the hardluck stories of the racing year so far when she was a race-day scratching from the Magic Millions Classic, Assail is setting an unlikely course towards Rosehill next month.

"She is definitely heading in the right direction but she's still got to do it," Robl said.

"You're not there until you're there ... that's the thing.

"And even when you think you are, the Magic Millions showed us you can never be certain until you run them off through the barriers."

Thanks to the painstaking efforts of trainer Clarry Conners, Assail confirmed she is over a hoof injury when she was kept on the bit to win a 900m heat.

On a track rated in the heavy range, Assail posted 54secs, the fastest on a morning in which top-class three-year-old Snitzerland and well-credentialled sprinters Tiger Tees and Pampelonne also won 900m trials.

Assail has been rated among the best of this season's two-year-olds to race in Sydney with two wins from as many starts.

She was a short-priced favourite to win the Magic Millions and she shares the fifth line of Golden Slipper as a $26 chance.

The Sweet Embrace Stakes, a Golden Slipper qualifier, is tipped to be Assail's comeback race.