Led Zep stars Jimmy Page, 65, Robert Plant, 60, and bassist John Paul Jones, 63, have been approached.

They played their only concert in 19 years at the O2 in 2007 and are seen as one of the few acts who could rival Jacko. His This Is It tour was due to start at the London venue on July 13.

AEG face multi-million pound losses if they cannot fill the slots. A source said: "Only Michael Jackson could sell out 50 nights at such a big arena, but Led Zeppelin and Abba combined might just rival him. There is huge money on the table."

According to the Los Angeles Times, AEG had invested a reported $20 million in production costs for the shows, billed as the "This Is It" concerts, which were scheduled to begin on July 13. AEG's profits for the concerts were expected at around $115 million, with a three-year worldwide tour also planned that could have grossed $450 million.

In a statement released Friday afternoon, AEG President & CEO Randy Phillips said, "Yesterday was a day I will never forget, or want to remember. Michael was both weak and strong, clever and kind, talented beyond belief and equally insecure. He was a doting father, respectful son, loving brother, and caring uncle. He was my friend. I take great solace in the pride and confidence he exhibited during production rehearsals on Wednesday night. That is the memory I will cherish for the rest of my life."

Despite rumors that Jackson had been falling ill, a source close to Jackson told MTV News, "Michael has been in rehearsals. He's been in good spirits. He's been rehearsing eight hours a day for the London concerts."