The show has suffered teething problems, with producers struggling to line up top-name acts for the tribute, hosted by actor Jamie Foxx and British TV host Fearne Cotton.
The Black Eyed Peas pulled out of the lineup this week, citing "unavoidable circumstances" amid reports the chart-topping band is splitting up.
Organizer Chris Hunt said that despite the last-minute loss, fans could expect "a very, very spectacular show."
"Everything we've done has been governed by one criterion — would Michael have done it this way, would he approve, would he like it?" said Hunt, chief executive of Global Live Events. "We're trying to do something worthy of one of the greatest showmen of modern times."
Several fan groups around the world have criticized the event, not just for its timing, but for ticket prices that started at about $100 and for what some regard as an out-of-the-way location in Cardiff, 150 miles (240 kilometers) west of London.
Organizers also outraged many fans by inviting the rock band Kiss, whose bassist Gene Simmons told a magazine last year that there was "no doubt in my mind" that Jackson, who was acquitted of molestation charges in 2005, had abused children.
The invitation was hastily rescinded, but many fans remained angry.
"The fans are not happy that the Jackson estate is not involved," said Wesley Noorhoff, president of a Dutch Michael Jackson fan club. "It seemed like they wanted to build a concert soon, to get money.
"I believe it should wait, not only because of the Murray trial. If you do a tribute to Michael, it has to be the best there is, just like Michael."
Hunt insisted the show would be a success. He said more than 40,000 tickets had been sold by Friday, and he was confident of reaching the venue's 50,000 capacity.
Some of the proceeds will go to the AIDS Project Los Angeles and Prince's Trust charities, and a portion will be placed in a trust fund for Jackson's children, though organizers did not give an exact breakdown.
Marlon Jackson, 54, said he wanted dissenters to know that Michael would have approved of the show.
"I want the world to understand that my brother was more than just an entertainer," he said. "There was a human side to him as well."
Jill Lawless can be reached at: http://twitter.com/JillLawless
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