Paula Radcliffe admits her chances of appearing in the Olympic marathon on 5 August are "not looking good".
The 38-year-old will have a final test this Sunday to see whether her injured foot will allow her to compete.
The Mail on Sunday newspaper claimed she would not run, prompting an angry Twitter response from the Briton.
She wrote that she was "hurt" by the story, admitting it was "not looking good" but insisting it was her "heartbreaking news to break".
British Olympic chef de mission Andy Hunt and UK Athletics insisted no decision had been taken on Radcliffe's particpation.
"There is nothing to say she is out," said Hunt. "Right now, she is in the team."
A UKA spokeswoman added: "No decision has been taken. The team are continuing to work with Paula and monitor her."
The chances of Radcliffe competing were rated 50-50 last week by UKA head coach Charles van Commenee.
She has been dogged by osteoarthritis during her career and revealed she was suffering again earlier this month, leading to a trip to Germany for specialist treatment.
Radcliffe is the world record holder in the marathon and a former world champion, but she has had an unhappy time at the Olympics.
She has missed out on a medal in four appearances between 1996 and 2008, her best performance coming on the track at the Sydney Games in 2000, when she was fourth in the 10,000m.