A decision on when the London Marathon can be held has been pushed back to 7 August.
An announcement had been expected on Tuesday on whether a socially distanced Virgin Money London Marathon could be held on Sunday, 4 October.
However, London Marathon Events has delayed the decision.
In a letter sent from Hugh Brasher, the event director to all the participants it said that the delay was due to a need for further consultation with local NHS Trusts, the emergency services and local authorities.
Brasher said: "I realise that this uncertainty is far from ideal and I would like to thank you for your patience and understanding in these very challenging circumstances.
"We know how important the Virgin Money London Marathon is to you, to charities and in showing the world the wonderful spirit of London, of Great Britain and of our running community.
"So please bear with us while we finish the extensive work we have been doing to try to enable us to run together, safely."
Guidelines on the return of mass participation running events in the UK were published on Tuesday, 21 July with the first races expected to go ahead under the new regulations in August, September and beyond.
