Trainer Phillip Stokes says the Jim Moloney Stakes at Caulfield will determine the spring path of Assertive Play.

Options after Saturday are the Thousand Guineas at Caulfield next month or a freshen for shorter course races.

After winning her first two starts at Morphettville over 1050m and 1100m in June, Assertive Play had her first Victorian start with an unlucky fourth in the Atlantic Jewel Stakes at Moonee Valley on September 8.

Stokes said Saturday's 1400m contest was the perfect opportunity to test the filly at a trip beyond 1200m.

"We're running her at the 1400 metres because we're not sure what her distance range is," Stokes said.

"We're not convinced she's a miler, so this will give us a good guide.

"We always thought she was a 1000-metre horse, but at the back of my mind I'm wondering if she likes that 1200-metre hot speed.

"If we run her this Saturday we've still got time to freshen her up for something else or if we decide to go to the Thousand Guineas we've got three weeks to get her there.

"This will give us a good indication of where we are at."

Stokes said Assertive Play had been stabled at Caulfield since her Moonee Valley performance and was in top shape for Saturday's race.

"I can't fault her. She needs a good speed on so here's hoping for Saturday," he said.

While unsure whether Assertive Play will be a Thousand Guineas contender, stablemate Music Bay is on track for the Group One race for three-year-old fillies.

Music Bay resumed with a second placing behind the unbeaten Newcastle filly Smart Melody at Flemington last Saturday and will have her next start in the Thousand Guineas Prelude on September 30.

"I'm confident she'll get out to the mile and in the autumn be an Oaks filly," Stokes said.