Defending champion Paula Radcliffe has withdrawn from the Flora London Marathon on April 23 with a foot injury.
The same problem which forced the world marathon record holder to miss the recent Commonwealth Games 10,000 metres in Melbourne will prevent her chasing a fourth London title.
"I am really disappointed to have to miss this year's event," said Radcliffe, 32.
Radcliffe had been preparing for the race at altitude in Albuquerque, New Mexico.
She added: "The Flora London Marathon is something that is extremely important to me, and I have done everything possible to resolve the problem and get to the start line.
"I have to accept that the injury needs a short period of total rest and I also have to focus on moving on from this and on my future."
Race director David Bedford added: "After she withdrew from the Commonwealth Games 10,000m, it was always a possibility that Paula would pull out of London.
"To race when less than fully fit is simply not the Paula we know and could jeopardise her form for some time.
"We fully understand that this is the right decision and look forward to welcoming Paula back in the future.
"The Flora London Marathon will still serve up two great races on April 23 and, if anything, the women's race will be all the more intriguing now."
Adding to British woes, the country's leading male distance runner Jon Brown - who placed sixth last year - will also miss the race.
Brown has been beset with injury problems during his career and has been a regular fourth-placed finisher at major championships, including the last two Olympic marathons.
He improved his six-year marathon best when retaining his AAA title in London last April with a time of two hours, nine minutes and 31 seconds.
Brown said: "I have been suffering from a foot problem recently which is clearing now but has left me way behind in my training preparations for London.
"I feel like I have only done two-thirds of the training needed, and I know this isn't enough for London as I cannot expect to perform to the level I feel I should.
"This is disappointing for me especially as this year's race looks to be such a great one. I wish everyone all the best for a successful race."
Bedford declared: "Jon is as thorough in his preparation for his major races as anyone and he has clearly left this announcement as late as possible to give himself every opportunity to make the right decision.
"We know he would not want to come to London if he could not do himself justice. We wish him well for a speedy return to full fitness and a successful summer."
A late signing for the meeting is Abdelkader El Mouaziz, the Moroccan winner of the race seven years ago who will be making an eighth appearance in London and was fourth last year.Reuse content