I'm not quite ready enough - Radcliffe
Britain's Paula Radcliffe has withdrawn from the World Championships marathon in Berlin on Sunday.
The 35-year-old underwent a foot operation in March and returned to action with victory in the New York City Half-Marathon on Sunday.
But, despite flying to Germany that evening, Radcliffe admitted she was not ready to compete over a full marathon.
"I am devastated I wasn't ready in time, especially having got so close in such a short time frame," she said.
"When I do my first marathon back I want it to be a good one and keep going with good ones through to London 2012, building positively. I don't want to feel like I'm reaching to get ready and have a little setback.
"I am feeling good about the repair work they've done on my foot and the way everything's feeling. I want to stay healthy, enjoy races and get back to racing as often as I used to be able to in the run-in to 2010."
It won't be the track in 2012, it will be the marathon. It's already going through in my mind; you already start the visualisation now. It's definitely the marathon
Radcliffe admitted to feeling she may have let people down but the sense of wanting to do herself, and her supporters justice was key in her decision.
"I don't want to be selfish but I've got to put myself first because people would rather see me winning in 2010 than here," she said.
"With an event like the marathon you have to be ready for it. It's a hard event on your body and mind so you need to be 100%."
She dismissed suggestions that running in New York was a mistake, saying this was part of her recovery process to ascertain the extent of her readiness for Berlin.
"Running in New York was a necessary part of the process," she said. "Had I not done that, the decision would have be 'no' 10 days ago.
"The only way to really know is to test things out and see how you come through it. I needed to ask though questions to be sure."
Radcliffe, who finished 23rd in the 2008 Olympics marathon, won gold in the marathon at the 2005 World Championships in Helsinki but she will now have to wait at least another two years to reclaim that title.
However, having made the correct decisions in the short-term Radcliffe feels this will enable her to compete more in the future, with the long-term target the marathon at the 2012 Olympics.
"Certainly I believe you'll see me racing more often than I have been able to the last couple of years, whether that's on the road or the track," said Radcliffe.
"It won't be the track in 2012, it will be the marathon. It's already going through in my mind; you already start the visualisation now. It's definitely the marathon."
BBC Sport's Sonja McLaughlan spoke to Radcliffe on Thursday and said that despite her victory in New York, the three-time London Marathon winner had an immediate gut feeling that she would not be ready in time for the World Championships.
Radcliffe has been running in Berlin twice a day and said that if the marathon was next Sunday, she would have made it.
UK Athletics head coach Charles van Commenee added: "To lose an athlete of Paula's calibre is disappointing to say the least.
"She won the World Championships in 2005 and a fit Paula would clearly be in contention to regain that title, but she has taken that difficult decision and we have to respect that."