Dettori had been set to ride competitively for the first time since November on Monday at Leicester but is yet to be granted a new licence by French horse racing chiefs.
France Galop say they need to speak to the 42-year-old about “medical issues”, without elaborating, while Dettori’s camp say it is a “private matter”.
Either way the Italian-born three-time Champion Jockey is running out of time to accrue necessary race practice before the Epsom showpiece on 1 June.
Dettori, who won the Derby in 2007 aboard Authorized, has been working at Aidan O’Brien’s Ballydoyle headquarters and had an outside chance of earning a late booking on one of the trainer’s four entries.
France Galop have cleared Dettori to ride in Britain, but their qualified statement led to the British Horseracing Authority scrapping the jockey’s comeback appearance.
“The BHA is awaiting either clearance from France regarding Frankie Dettori or an understanding of the reason why France Galop does not consider him fit to ride,” said BHA spokesman Robin Mounsey.
“At present France Galop is exercising its right not to disclose this information. Clearance from France was always one of the criteria needed before Dettori could be issued his licence to ride in Britain and this was made clear.”
Dettori’s camp are understood to be frustrated by France Galop’s approach, having booked in further rides at Nottingham on Tuesday and Lingfield yesterday.