Alex Ferguson's colt Rock Of Gibraltar is set to miss York's Ebor Meeting.
The Aidan O'Brien-trained colt is "on a break" after several of his Classic generation were affected by coughing.
The multiple Group One winner equalled Mill Reef's record of six consecutive victories at the highest level when he won the Sussex Stakes at Goodwood last week.
O'Brien told the Racing Post: "York is now off the agenda for Rock Of Gibraltar, who is on a break together with many of the other three-year-olds."