Japanese swimmer Rikako Ikee, a medal favourite for the Tokyo 2020 Olympics, has been diagnosed with leukaemia.
The 18-year-old won a record six gold, plus two silvers, at last year's Asian Games in Indonesia.
Ikee, who had left a training camp in Australia, announced the diagnosis on social media and said she is "in a state of confusion".
"I will devote myself to my treatment and strive to be able to show an even stronger Rikako Ikee," she said.
Ikee has withdrawn from the Japanese championships in April.
She is a former world junior 50m freestyle, 50m butterfly and 100m butterfly champion and was likely to be a strong medal favourite at July's senior World Championships in South Korea.