Organisers Global Live Events were due to make an announcement at 6pm this evening, but the press conference has now been cancelled.
A statement on the official Michael Forever – The Tribute Concert Facebook page: “We will wait with the announcement until we can name the new headline act.”
Global Live Events, meanwhile, have tried to appease fans after uproar over their ticket sales policy.
The company claims the ticketing system is designed to deter touts from hiking up ticket prices to rip off fans – even though it will still result in buyers spending extra.
“If more people want tickets than are available the price goes up,” a new frequently asked questions section of the official Facebook page explains.
“With our system the initial demand is moderated by the charity pledges.
“We don’t get the extra money – the charities do. So all the profit that a tout would usually take has already been given to the charities.
The firm tries to explain away the decision to hold the show in the midst of the trial of Jackson’s doctor Conrad Murray – charged with the star’s manslaughter – which enraged his singing brothers, Jermaine and Randy.
“We have been planning this concert for quite a while, and the trial dates kept moving,” the site says.
“Unless the trial dates change again the concert will take place a month into the progress of the trial.
“We believe that a concert honouring Michael’s music will remind the world of his genius, and the great loss the world of music has suffered by his untimely death. But the concert and the trial of the doctor have no bearing on each other.”
The firm said of the Jackson family rift: “The Jacksons are a large family with differing views and opinions on how to treat the memory of Michael.
“We believe, and the vast majority of the family believe, that the Michael Forever tribute concert, which will be about Michael’s music, is the best way to do this.
Check back later today for the concert line-up.