Dina Asher-Smith has said she is pulling out of the 200m after failing to qualify for the 100m final.
The 25-year-old, the fastest British woman in history, had eased through qualifying on Friday but came up short in today's semi-final.
Asher-Smith was seen as having a good chance of ending Britain's 60-year wait for an individual women's sprint medal.
The Londoner picked up a hamstring injury in the run-up the Games and said after the race she "was not her normal self" as she tearfully announced she would pull out of the 200m.
She is the current world champion in the event.
Speaking to the BBC, Asher-Smith said she had been trying to recover from a torn hamstring - which doctors first thought might need surgery.
She said she had "turned over every single stone to make sure I can stand on the line".
"Obviously I'm so disappointed not to make the final because this is Tokyo 2020, it's everything I've trained for for the past two years," she said.
"But the last few weeks of my athlete life have been absolutely insane."
Asher-Smith finished behind defending champion Elaine Thompson-Herah and Switzerland's Ajila Del Ponte in her 100m semi, with only the top two going through automatically.
She then had an anxious wait to see the times from the following two heats, but her 11.05 seconds was not enough.
However, there was joy for Team GB's Daryll Neita, who finished third in a separate semi-final and qualified as one of the fastest losers with a time of 11.00 seconds.
She came eighth in the final - which was won in a new Olympic record of 10.61 by Jamaica's Elaine Thompson-Herah.
It was a clean sweep for the country, with Shelly-Anne Fraser-Pryce second and Shericka Jackson third.
Elsewhere, Team GB had more success on Saturday, winning two more golds in the mixed swimming medley and triathlon events - and two bronze medals in windsurfing and boxing.