"Due to unavoidable circumstances, the Black Eyed Peas will be unable to perform at this Saturday's Michael Forever event," said Chris Hunt, head of Global Live Events which is staging the concert.
"It is with regret that we announce the removal of Black Eyed Peas from the Michael Forever bill, but I look forward to a great night with other earth shattering artists," he added.
The announcement immediately triggered widespread reports that the hip-hop quartet were about to split.
Pop singer Christina Aguilera and Motown legend Smokey Robinson will head Saturday's line-up at Cardiff's Millennium Stadium, but the concert has been overshadowed by the trial of doctor Conrad Murray, who is accused of Jackson's manslaughter.
A rift has developed between family members over whether they should attend the concert or remain in Los Angeles for the trial.
The event is the brainchild of brothers Marlon, Tito and Jackie, sister La Toya and mother Katherine but siblings Jermaine, Randy and Janet remain opposed.
Michael Jackson's three children, Paris, Blanket and Prince, are all expected to attend.
There has also been dispute over where proceeds from the concert will eventually end up.
A portion of the takings will go the AIDS Project Los Angeles and Prince's Trust -- both charities supported by Michael Jackson -- but many fans have been angered by reports that the Jackson family themselves stood to make a profit.
Amid the chaos, ticket sales have reportedly been slow with many areas within the 60,000 capacity venue likely to remain empty.
Other acts scheduled to perform include singer-songwriter Cee Lo Green, British singer Leona Lewis, pop act JLS, R&B star Craig David and rock band Alien Ant Farm.
Beyonce is due to perform via satellite link from the US.
For fans who cannot attend, the show will be broadcast to 30 countries in both 2D and 3D.
"Billie Jean" megastar Jackson died in Los Angeles in 2009 aged 50 while rehearsing for a series of comeback concerts to be held in London.
Copyright AFP (Agence France-Presse), 2011