Rio 2016 gold medallist Wayde van Niekerk failed to reach the final of the 400m at the Olympic Games Tokyo 2020 on Monday (2 August).
The South African, who set a world record of 43.03 in taking victory five years ago, has struggled with a succession of injuries since tearing his anterior cruciate knee ligament in October 2017.
The 29-year-old has struggled for form and recently moved to Florida to train.
In the third semi-final of the 400m, van Niekerk was in contention on the home turn, but faded into a distant fourth place behind reigning world champion Steven Gardiner of the Bahamas, and USA's Michael Norman.
Van Niekerk's predecessor as Olympic champion, Grenada's Kirani James, was the fastest qualifier with a time of 43.88 seconds.