St Patrick's Day, a full brother of US Triple Crown winner American Pharoah, makes his Irish debut in this eight-runner event having joined Aidan O'Brien from Bob Baffert for a European campaign.
He ran twice at Del Mar last year, winning a 6½f maiden there on his second start in September. However, he picked up a tendon injury and has not raced since.
O'Brien said on Wednesday: "St Patrick's Day is a lovely colt and very straightforward. He's just ready for a run and however he gets on there should be plenty of improvement to come."
Although St Patrick's Day is entered for the Commonwealth Cup at Royal Ascot on Friday week, O'Brien, who is also represented in the Group 3 event by Full Moon, said: "We left St Patrick's Day in the Ascot race but we're not looking beyond Leopardstown and we're just hoping he runs a good race."
Seamie Heffernan rides St Patrick's Day, who wears a tongue-tie, with Donnacha O'Brien on Full Moon, who is being dropped in trip.
The Johnny Murtagh-trained True Valour, third in the Amethyst Stakes at Leopardstown and in the Diomed Stakes at Epsom on his two starts this year, drops in trip to 7f for the first time this season and will wear first-time cheekpieces.
Ger Lyons is represented by smart sprinter Ardhoomey, who steps up to this distance for the first time in three years, and Medicine Jack, whose three wins have been over 6f.
Jim Bolger, who has sent out seven winners of the event, most recently in Flight Risk a year ago, runs Smash Williams while Fas, a Group 3 winner over 6f in France last year, will be racing over the distance for the first time on his second start for Eddie Lynam.