Sir Percy bids to become the first horse since Roberto 34 years ago to follow up his Derby triumph in the Vodafone Coronation Cup 12 months later.
Marcus Tregoning’s stable star faces six rivals in the Group One contest for older horses at Epsom on Friday.
He has been lightly-raced since his short-head victory over Dragon Dancer but showed he had trained on when an encouraging fourth to Vengeance Of Rain in the Dubai Sheema Classic at Nad Al Sheba in March.
Opposition includes Sixties Icon, who although only seventh in the Derby went on to win the St Leger. Jeremy Noseda’s colt made a pleasing return to action with victory in the Jockey Club Stakes at Newmarket in May.
Scorpion, the 2005 Leger winner, is one of two runners from the Aidan O’Brien stable, the other being Septimus.
The in-form Maraahel attempts to give Michael Stoute a fifth Coronation Cup success while Clive Brittain tries for a third with Hattan.
The field is completed by the John Best-trained Rising Cross, who was runner-up to Alexandrova in the Oaks last year. She bids to become the first filly to win the race since In The Groove in 1991.
The four horses taken out at the 48-hour final declaration stage were the O’Brien duo Yeats and Dylan Thomas, along with Cherry Mix and Irish Wells.