One of the sensations of the World Cup.
"If you had to pick a world XI at the moment, Duff would be there," Leeds boss David O'Leary told BBC's Match of the Day on Sunday.
And who could argue after watching the Blackburn forward torment a succession of defences at the World Cup?
Duff was a threat in attack, where he started Ireland's four matches.
But it was when switched to the wing, his club position, that he really came into his own.
Duff terrified full-backs such as Spain's Juanfran with his ability to race away on the outside or cut in and head for goal.
Blackburn boss Graeme Souness says he will not let the prodigiously talented 23-year-old go, but with the likes of Liverpool, Manchester United and AC Milan on his trail he might have to.