The "Thriller" singer – who has already had to postpone the first four dates of his 50-night residency at London's O2 arena – may have to undergo intense radiotherapy treatment meaning he will not be fit to perform for the scheduled dates in July.
A source close to Jackson – who is said to have already had potentially fatal growths removed from his nose and arm – told Britain's The Sun newspaper: "Michael has a devil of a decision. The temptation is to go for treatment which will allow him to perform."
"The last thing he wants to do is let his fans down. But it may be that radiation is still needed. That can have nasty side effects and leave him unable to sing."
Although the 50-year-old star's spokesman insists he is in great health, doctors are apparently worried about a patch of cancerous skin on his chest.
They may be able to remove it layer by layer, meaning he would still be able to perform, but radiotherapy would be a lot more effective.
Last week, it was revealed Jackson would kick off his concert run on July 13, five days later than originally planned.
Shows scheduled to take place on July 10, 12 and 14 have been moved to the end of the residency in March 2010.
Randy Phillips, president of AEG Live who are promoting the tour, has dismissed Jackson's rumored cancer battle and stressed the delay is down to preparations for the "massive and technically complex show."
