Ireland will be without Rhasidat Adeleke for the women's 4x400m relay at the World Championships in Hungary.
The 20-year-old said she felt "so fatigued" and needed a break after finishing fourth in the 400m final on Wednesday night.
The decision was reached by "team management, with a duty of care to all athletes in mind".
It was taken after "consultation with Adeleke and her coach" and team medical staff, said Athletics Ireland.
Sharlene Mawdsley, Sophie Becker, Roisin Harrison, Kelly McGrory and Niamh Murray all remain available for selection ahead of Saturday evening's heats.
The Irish team will be aiming to produce another strong performance before targeting Olympic qualification at next May's World Relay Championships in the Bahamas, where 14 of the 16 available spots will be filled.