"Owing to the urgency, NASA Summit is handling, our consultations are on-going and progressing well," Chief campaigner Musalia Mudavadi.
He said in a statement that the address will be delivered on Wednesday.
"We regret that the consultations are taking longer than anticipated. NASA will, therefore, not address Kenyans as projected today."
Opposition leader Raila Odinga said they were going to make a major announcement today.
This was after he was defeated by incumbent Uhuru Kenyatta in Tuesday last week's election.
IEBC figures showed Uhuru won with 54.3 per cent of the vote, ahead of Raila who had 44.7 per cent.
Nearly 80 per cent of the 19 million registered voters cast their ballots according to results declared by IEBC on Friday last week.
Raila on Sunday called for a nationwide work boycott in push for his claim to the presidency.
He accused Jubilee administration of "spilling the blood of innocent people".
The ODM leader is under pressure locally and internationally to concede defeat to Uhuru.
He has brushed off the pressure.
NASA said the whole vote was rigged, and thatJubilee Party has conspired with security forces to crush dissenting voices.
He doubled down on his attacks in a speech to hundreds of cheering supporters in Kibera and Mathare.
-the Star