The talented-but-fragile three-year-old ran Churchill close in his juvenile season and landed the Desmond Stakes last time out.
Stack, though, would have no qualms about pulling him out if the heavens opened.
"He seems in good shape, but this is obviously another step up in class," said Stack. "Everything has gone smoothly since then, it's always been a day-by-day thing with him. Hopefully we'll have no more rain, if it went heavy we'd have to think about running him.
"We'll keep him at a mile this year, hopefully he stays in training next year when we might think about stepping up."
One-time Derby hope Sir John Lavery looks the one to beat. The Galileo colt cut little ice in the Lingfield Derby Trial and the King Edward VII at Royal Ascot but dropped in trip last time out, he looked the real deal.
Aidan O'Brien's charge may have only won a Listed race at Cork but the manner in which he did it suggested he was in for a fruitful autumn.
"When we brought him back (in trip) at Cork, we were obviously delighted with him. We were obviously going the wrong way," said O'Brien.
"He was very comfortable going that pace, so we're looking forward to him and looking forward to seeing how he goes on Saturday."
David O'Meara runs Suedois and Custom Cut, with Psychedelic Funk wearing first-time blinkers for Ger Lyons.
In the KPMG Enterprise Stakes, O'Brien saddles Spanish Steps, Exemplar and last year's Derby runner-up US Army Ranger, who has been running over extended trips this season.
"Spanish Steps won a Group race at Leopardstown on some nice ground and he went to York after that where he was a little bit disappointing on soft ground, so the better the ground the more it will suit," O'Brien told At The Races.
"A very straightforward, decent, honest horse. Group Three level should be well within his compass, maybe even Group Two and possibly Group One in time.
"We liked Examplar last year, but he's been disappointing this year. He's lazy at home, so he's in blinkers, they help at home - the trip is unknown.
"US Army Ranger has been frustrating, I placed him badly, I'd say. You'd imagine he'd stay, but some things haven't been right with him. We're on a recovery mission with him."
O'Brien's Delano Roosevelt created a huge impression on his debut and steps up for the Willis Towers Watson Champions Juvenile Stakes.
"He's a lovely horse, he'll stay very well and is probably a middle-distance horse for next year," said O'Brien.
"He's probably a little bit of a baby still and he will improve a good bit more for the run, but it's at a great track, one he's won on, and we'll learn a good bit more about him and he'll learn more about racing.
"He's out of a very good mare (Again) and by Galileo, so he's an exciting horse. Win, lose or draw, the run will do him good for the rest of the year and next year."
Mick Halford's Riyazan brings a similar profile, with the trainer looking forward to the next step.
"He won like a smart horse and it's not like one of ours to pick up and quicken like that first time out," he said.
"He lugged across the track a bit, but it was only through greenness. He's had a trouble-free run since."
Elsewhere on the card, Ruby Walsh has his first ride on the Flat for four years on top-weight Renneti in the Irish Stallion Farms EBF "Petingo" Handicap.
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