Laura Muir and Jemma Reekie have quit their training camp in South Africa – just 15 months before the Olympics.
The pair have returned to the UK and are training at Loughborough after an apparent falling out with coach Andy Young.
The pair have just under five months to go until the World Championships in Budapest.
A UK Athletics spokesperson said: “UK Athletics can confirm that Laura Muir and Jemma Reekie left their altitude training location last week to return home to the UK.
“World Class Programme staff and services are continuing to work with both athletes to ensure they receive the support they require as they review their training and competition programmes for the season ahead.”
Under Young, Muir has won Olympic 1500m silver, world 1500m bronze, two European Championships titles and five European Indoor crowns.
Reekie finished fourth in the 800m at the Tokyo Olympics and was fifth in the 800m at last year’s European Championships and in the 1500m at the Commonwealth Games.
“There was no bust-up,” Young told The Times. “I think you would find the girls were worried about my health if you spoke to them.
“(They) felt I wasn’t looking after myself properly, maybe thought pressure was getting to me. I’d say they were reading too much into it.”