The 38-year-old recorded her slowest time over the distance, finishing in one hour, 12 minutes and three seconds, in a race which had been billed as a head to head between Radcliffe and Haile Gebrselassie.
Radcliffe finished over 11 minutes behind the Ethiopian double Olympic champion after receiving a head start of almost eight minutes, and admitted her struggles could not solely be attributed to a bout of bronchitis for which she has been taking anti-biotics.
"I just didn't really feel good after six or seven kilometres," she told BBC Sport.
"My legs just wouldn't move properly and I was fighting harder than I should have been just to keep moving.
"I could see the pace dropping rapidly off and then I just decided I wasn't going to look any more because the format of the race meant stopping wasn't an option even though I felt really bad."
Asked if she had been affected by the virus, she said it was a "factor".
"I didn't expect to feel 100% but I didn't expect to feel that bad either and that's what's worrying me a little bit," she said.
"The thing that worries me is that I didn't feel like myself out there running and so that obviously worries me because I want to feel like that (like myself) this summer."
Radcliffe is hoping to make her third attempt to win an Olympic medal at London 2012 after failures in Athens and Beijing.
And asked if she was worried about her Olympic chances, she added: "I'm not giving up on it by any means.
"There are reasons, I just didn't expect those reasons to make that much difference.
"The danger is more that it affects my confidence, you could be starting from zero now and still be in shape by the Olympics."