Gomez is among the top rank of jockeys in America and has ridden over 130 winners this year.
The ride on Ivan Denisovich in the Secretariat Stakes on the same card has gone to John Velazquez.
A disappointed Fallon has returned to Ireland after being refused a licence by the Illinois Racing Board.
He took the case to the courts in Chicago but his legal representatives failed in their bid to have an injunction granted against the decision which was made due to the current allegations hanging over him regarding alleged race-fixing charges.
Prohibited under the order from even going to the track at Arlington Park, Fallon was soon on a flight back home, where he will be in action for O’Brien at the Curragh tomorrow.
Meanwhile, Alan Swinbank’s Collier Hill spearheads a two-pronged British assault on the Group One Rheinland-Pokal der Sparkasse KolnBonn at Cologne tomorrow – a race in which Mark Johnston’s Bandari finished second last year.
The eight-year-old gelding turned in arguably a career-best performance when coming second to Heart’s Cry in the Dubai Sheema Classic at Nad Al Sheba in March.
Last season’s Irish St Leger winner joins Godolphin’s Cherry Mix and David Wachman’s Irish raider Fracas in the mile-and-a-half contest.
Dean McKeown is looking forward to riding Collier Hill. “I rode work on him last week,” said McKeown. “He worked nicely.”