It had been widely expected that the song would be made available to buy from digital retailers such as iTunes from Monday.
Merchandising
Jackson's official website described it as a "brand new single", which would be "released" on 12 October.
But a spokesperson said the term "released" referred to its distribution to radio stations and other media outlets.
The song takes its name from the ill-fated series of comeback shows that were to have taken place at London's O2 arena.
It will also feature in the closing credits of a film, also called This Is It, which has been made using footage of rehearsals for the O2 concerts, due to be released in cinemas on 28 October.
The BBC's Peter Bowes in Los Angeles says it was widely known that Michael Jackson had huge debts and those debts have not gone away.
But, he says, what he is hearing is the money that will be made from this single, from the movie and lots more merchandising that will take place will easily pay for all those debts and there will eventually be money left over that will go to Michael Jackson's mother and his three children.
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