Radcliffe, 34, would be Britain's best bet for gold were it not for a stress fracture in her left thigh, which has reduced her chances even of competing in Beijing.
She is allowed until the eve of the women's marathon, which starts at 0030 BST on 17 August, to make a decision on her fitness.
Despite a stellar record that includes world marathon gold in Helsinki in 2005, she has never won an Olympic medal in three previous visits to the Games.
In Athens four years ago she pulled out in tears, exhausted, part-way through the marathon.
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