Paula Radcliffe admits she faces a "race against time" to be fit for the Beijing Olympics in August.
The 34-year-old was in London on Monday to meet with UK Athletics officials and undergo tests at the British Olympic Medical Institute in Northwick Park.
She has now returned to the French Pyrenees to continue high-intensity training at her base in Font Romeu.
"I'm going back to continue my training - but yes, it is going to be a race against time," Radcliffe said.
The marathon world record holder's participation is threatened by a stress fracture in her left thigh.
Her injury was diagnosed in May and having attended her first meeting with UK Athletics medical officials since that "bombshell" news it is understood Radcliffe is progressing well in her recovery.
The British Olympic Association had already named Radcliffe in its team, and UK Athletics performance director Dave Collins said she would be given until the last minute to prove her fitness.
"She is working as hard as she can," he told BBC Sport. "It is a very challenging injury and Paula is doing the best job.
"She has said she is making progress and we are very happy to be able to offer her the most support we can to get her there."
Athletes can drop out at any time on medical grounds and be replaced, and Radcliffe could leave it as late as the night before the race on 17 August to decide if she is fit enough to run.
"I will keep in close contact over the next few weeks to see if there is a need for me to go out to Beijing"
Glasgow-based Hayley Haining is on stand-by should Radcliffe fail to overcome her injury in time.
"It is not a nice situation to be in, where you could be taking the place of an athlete who is injured and has earned the right to be there," Haining told BBC Radio 5 Live on Monday.
"At this stage they have to know either way if she is breaking clear of the injury, and if Paula is cleared to go, I would say 'good luck' and I hope she does really well.
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Olympic gold is still missing from Radcliffe's impressive CV following her dramatic failure at the 2004 Games in Athens.
One of the favourites going into the race, she withdrew in tears at the 23-mile mark.
She attempted to win a medal in the 10,000m a few days later but dropped out of the final with eight laps left, later revealing she had been suffering from a quad injury and a stomach upset.
Radcliffe returned to win the 2005 London Marathon and took gold at that year's World Athletics Championships, before triumphing in the 2007 New York Marathon following the birth of her first child 11 months earlier.
She withdrew from the 2008 London Marathon citing a toe injury, then had a hip problem which further scans in May revealed to be a stress fracture of the left femur.
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