LONDON: They say the star is 20lb underweight and urgently needs to pile on the pounds ahead of the 50 live shows, from July 8 to February 24.

Jacko, 50, is also undergoing antibiotic treatment for a skin infection, still suffers pain from an old back injury and wears a mask to avoid picking up bugs.

Promoters AEG Live last night insisted Michael is “extremely fit” and looking forward to his shows.

But privately there are fears he may not be able to keep up with the gruelling dance routines.

A source said: “There are concerns Michael is too frail. He has been ordered to eat more but he refuses to and eats like a bird.”

Jacko has not performed since a disastrous slot at the 2006 World Music Awards, when he only managed to sing two lines of We Are The World.

He has been rehearsing for his farewell shows at a heavily guarded LA hangar — and is reportedly insisting on having live animals on stage with him.

He also wants to perform a duet with 12-year-old son Prince.

It’s all shaping up to be suitably crackers.