Chris Waller is still not 100 percent sure what Riff Rocket’s entire Spring campaign will look like, but the dual Derby winner will be given his chance to prove he can be an elite-level open-age stayer.

The four-year-old American Pharoah gelding will be among the entries for the Cox Plate (2040m) and Caulfield Cup (2400m), both $5 million Group 1 events, when they close on Tuesday.

Riff Rocket became just the fourth horse to win the ATC Derby (2400m) in autumn after a spring win in the Victoria Derby (2500m) and Waller thinks he can be a Caulfield Cup force but will make a final call in the first weekend in October.

“Your fork-in-the-road is Epsom weekend (October 5), whether it be the Turnbull (Stakes), whether it be a weight-for-age 2000-metre race here (Sydney),” Waller said.

“Then they’re fit enough to go to 2400, which I think he would be. I’d say logistically he’d be going towards a Caulfield Cup.

“There’s so many options in the spring but he has won a 2500-metre and a 2400-metre Derby.”

Riff Rocket is a $15 second favourite behind Fawkner Park ($11) in Caulfield Cup betting and is a $26 chance in Cox Plate markets with bookmakers, which are headed by Pride Of Jenni ($4).

Tuesday morning’s Rosehill trials will mark the continuation of Riff Rocket’s Spring preparations, set to have his second trial of the campaign over 1000m.

He is down to contest the first trial, in which stablemate and leading Cox Plate contender Via Sistina is also engaged, alongside Tropical Squall and Pericles.

Another Waller star, Fangirl, headlines the second 1000m trial with James Cummings-trained Group 1 winners Zardozi and Tom Kitten among her rivals.

While the picture for the Caulfield Cup and Cox Plate will start to take shape on Tuesday, it is another month before the Melbourne Cup nomination deadline with entries for that event closing on September 3.