Frankie Dettori has picked up the plum ride on joint favourite Santiago in the St Leger at Doncaster on Saturday.
The 49-year-old, riding for trainer Aidan O'Brien, is seeking his seventh triumph in the world's oldest Classic.
O'Brien's principal jockey Ryan Moore will be at Leopardstown, where he has opted to ride Japan - rather than last year's winner Magical - in the Irish Champion Stakes.
Santiago is joint 11-4 favourite with Pyledriver, trained by William Muir.
Pyledriver, the mount of Muir's son-in-law Martin Dwyer, went unsold as a foal for £10,000 and now lines up for a Group One race with a first prize of nearly £200,000 and the potential for far more valuable breeding fees in the future.
Saturday's big race at Doncaster (15:35 BST) will be held behind closed doors after health officials halted a crowd pilot event at the course.
Leading contenders include Hukum, winner of the Geoffrey Freer Stakes at Newbury, who will bid to give his trainer Owen Burrows a first Classic victory.
In Ireland, the Godolphin runner Ghaiyyath - the world's highest-rated horse - heads the field in the main contest (16:10).