Reckless Abandon was a significant absentee from the 12 declarations for the Darley July Cup at Newmarket on Saturday.
Clive Cox's dual Group One-winning colt had been considered a major contender for this weekend's six-furlong feature having finished in Haydock's Temple Stakes before placing fifth in the King's Stand at Royal Ascot.
However, much to Cox's disappointment, the three-year-old suffered a late setback.
"He has a swollen gland just under his jaw and it looks like it will develop into an abscess," said the trainer.
"We had been very happy with his homework since Ascot, we'd been looking forward to Saturday and for this to happen is hugely disappointing for everyone.
"I'm not sure how long it will take for him to recover, but he'd been showing very positive signs since Ascot and hopefully we'll get him back on track."
Despite Reckless Abandon's absence, the Lambourn trainer still has a serious challenger for the Group One contest in Lethal Force, a most impressive winner of the Diamond Jubilee Stakes at the Royal meeting.
"He is absolutely fine," said Cox.
"I've been very happy with him since Ascot, I'm really pleased with him and we're looking forward to seeing him run again on Saturday."
Mike de Kock's South African challenger Shea Shea heads the July Cup market having been narrowly denied by Eddie Lynam's Sole Power in the King's Stand.
The two do battle over an extra furlong on the July course, while Lynam also has a fascinating second string in recent Curragh scorer Slade Power.
James Fanshawe runs Diamond Jubilee runner-up Society Rock and the Aidan O'Brien-trained Gale Force Ten comes back to sprint distances following victory in the seven-furlong Jersey Stakes.
Australian runner Shamexpress, Bahrain's Krypton Factor and Havelock from America give the race a truly international feel.
The field is completed by Hamza, Sovereign Debt and Zanetto.
Reckless Abandon was one of just three defections from the six-day stage, the others being outsiders Reply and Soul.