Simone Biles was admitted to hospital with a kidney stone on the eve of her return to international competition at the World Gymnastics Championships in Doha.
Biles, a 10-time world championship gold medallist, is due to compete in the women's qualification rounds on Saturday.
Yet on Friday evening, the 21-year-old could be seen on a hospital bed in a photo she uploaded to Twitter.
In text accompanying the image, Biles wrote: "nothing like a late night ER visit less than 24hrs before world championships ... this kidney stone can wait ... doing it for my team!
Biles took a lengthy break from competition after claiming four gold medals at the Rio 2016 Olympics.
At August's U.S. Gymnastics Championships, she became the first woman to take national all-around gold on five separate occasions, while also claiming golds in the vault, uneven bars, balance beam and floor events.