South Africa's Rio 2016 gold medallist and world record holder faded into fifth behind world champion Steven Gardiner.
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.