John O'Shea is taking a cautious approach to the return of Astern in the Silver Slipper at Rosehill.

Yet his choice of jockey might just give him up.

With Godolphin's No.1 rider James McDonald missing the Sydney meeting to ride Exosphere in Melbourne, Hugh Bowman will warm the saddle on Astern.

Trainer and jockey enjoyed a long and successful association before O'Shea took over as Sheikh Mohammed's private trainer and Bowman says his booking can only mean one thing.

"John tends to book me if James can't ride and he only gets me for the good ones," Bowman said.

"He tends to look for my services if he's got one who is above average."

Astern appeared just that at his only start in December when he posted an emphatic 2-1/2 length win over Niccolance at Randwick.

The runner-up franked the form with a second to Golden Slipper favourite Capitalist in the Magic Millions 2YO Wyong Classic.

Astern has opened odds-on favourite for the Silver Slipper with the Peter and Paul Snowden-trained Defcon the only other runner given a genuine chance.

O'Shea says Astern has matured since his initial campaign but warns he still has a way to go fitness-wise.

"He's just furnished a bit and he's a bit smarter," O'Shea said.

"If he was to win on Saturday we'd be really happy because he's got a lot of improvement."

Bowman travelled to Godolphin's Osborne Park property on the outskirts of Sydney to test Astern in trackwork on Tuesday.

He came away impressed.

"He's a very mature horse, a real two-year-old and he's got a beautiful temperament so he ticks a few boxes," Bowman said."