The Scottish couple left camp early and flew home, announcing on Friday that they had now separated from Young with immediate effect.
Under his tutelage, Muir had won Olympic silver in the 1500 metres, world bronze and European titles, while Reekie narrowly missed out on a medal at the Tokyo Olympics with a fourth-place finish in the 800 metres.
A statement released on Friday said: “UK Athletics (UKA) can confirm that Laura Muir and Jemma Reekie have made the decision to part ways with their coach Andy Young.
“Both athletes would like to thank Andy for his dedication and support over the years.
“They are now focused on making decisions around their support network and coaching setup for the future and will not be commenting further. UKA staff will continue to support the athletes during this time.