Concerns about extreme heat and a query over Riva De Lago's race fitness are likely to keep Chris Waller's new stable acquisition from resuming at Warwick Farm on Saturday.

Waller has entered the former Con Karakatsanis-trained galloper in the Sharp Flying (1200m) but says the gelding is likely to be saved for the following week.

"I probably won't run Riva De Lago," Waller said.

"He's a week away and there's an 1100 metre race at Rosehill the following week which is a bit short for him but timing-wise, it's better.

"And I'm scared of a 40-degree day with a horse that's only 90 per cent fit. I don't want to flatten him first-up in those type of conditions."

With temperatures expected to near 40 degrees at Warwick Farm on Saturday, stewards have altered the arrival time for horses on track to only one hour before their race.

While Waller said it was unlikely Riva De Lago would start, the trainer also has Coup Ay Tee in the event.

"He'll run and he's going well," Waller said.

"His best form has been away from Warwick Farm so that is a little negative for him but apart from that he's well and is racing very consistently."

The main race of the day is the Listed ATC Cup (Frank Underwood Cup) with Waller to saddle-up favourite Moriarty who he believes is well placed.