Simone Biles pulled out of the gymnastics women’s team final at Tokyo 2020 with what was later described as a “medical issue” before the United States went on to claim silver.
Biles, 24, briefly left the arena after scoring 13.766 on the vault in the first rotation – her lowest score on that apparatus in her Olympics career.
She was replaced by Jordan Chiles but returned to support her team-mates.
The Russian Olympic Committee team won gold, with Great Britain taking bronze.
There were no obvious signs of injury following Biles’ vault, in which she failed to stick her landing, but she returned from the treatment room appearing to flex her ankle, reports BBC Sport’s John Watson in Tokyo.
A statement from US gymnastics said: “Simone Biles has withdrawn from the team final competition due to a medical issue.
“She will be assessed daily to determine medical clearance for future competitions. Thinking of you, Simone!”
The US were the favorites for the team gold in Tokyo after winning five successive world titles – in 2011, 2014, 2015, 2018, and 2019 – in addition to their back-to-back Olympic gold medals in London and Rio.
They had to settle for silver, with Biles receiving a medal on the podium alongside Jordan Chiles, Sunisa Lee, and Grace McCallum.
Biles is the most successful US gymnast of all time and winner of four gold medals and a bronze at Rio 2016.
The 30-time Olympic and World Championship medallist needs four podium finishes in Tokyo to become the most decorated gymnast – male or female – in history.
She has reached all five individual finals and is next due to compete on Thursday when she will attempt to become the first woman to retain the Olympic all-around title since 1968.
Biles has been open about the pressure she feels in Tokyo, saying she feels like she has “the weight of the world on my shoulders at times”.