Fans urged Caster Semenya not to quit athletics after she posted a cryptic tweet following the loss of her appeal against regulations restricting testosterone levels in female runners.
Semenya will have to take medication to reduce her testosterone level if she is to continue competing at 800m.
The double Olympic champion, 28, posted picture on Twitter containing a quote hinting at retirement.
"Knowing when to walk away is wisdom. Being able to is courage," it read.
"Walking away with your head held high is dignity."
One person replied to Semenya's tweet saying "never give up" while another urged her to "fight until the end".
However, Semenya posted another tweet shortly afterwards that read: "That's me and will always be. I'm finished."
The Court of Arbitration for Sport (Cas) rejected the South African's challenge against new rules from athletics' governing body, the IAAF.
On Thursday, Lord Coe, president of the IAAF, welcomed the court's decision.
Speaking in a news conference for Friday's Diamond League meeting in Doha, he said: "It's pretty straightforward. Athletics has two classifications, it has age and gender.
"We are fiercely protective of both and I am really grateful the court of arbitration has upheld that principle."
Coe, who answered two questions on the subject before refusing to answer more and switching to the Diamond League, said there would be no delay in implementing the new regulations, despite Cas saying it had "serious concerns as to the future practical application" of them.
It means Semenya - and other athletes with differences of sexual development (DSD) - must either take medication in order to compete in track events from 400m to the mile, or change to another distance.
Semenya is still eligible to compete at the Diamond League meet in Doha on Friday and can make an appeal against the Cas ruling to the Swiss Tribunal Courts within the next 30 days.
Athletics South Africa (ASA) said it was "reeling in shock" at the decision and that the verdict "goes to lengths to justify" discrimination.
Meanwhile, Indian sprinter Dutee Chand, who fought and won a long battle over her own elevated levels of male sex hormones, said Semenya's court defeat was "wrong".
"I feel sad for her - she has been made to suffer like me," said Chand, who was cleared to compete last year after winning a court appeal against IAAF regulations.
"I think she and her team will find a way out. She is an Olympic medallist and her country is behind her."