Michael Jackson doesn't think he is fit enough for his 50 'This Is It' shows in London.

The 'Thriller' singer is 'angry' at promoters for booking the mammoth run as he never agreed to perform so many concerts at The 02 arena, which start in July.

Speaking to fans outside the Los Angeles studio where he is currently rehearsing for the shows, Michael reportedly said: 'I don't know how I'm going to do 50 shows, I'm not a big eater - I need to put some weight on.

'I'm really angry with them for booking me up to do 50 shows. I only wanted to do 10, and take the tour around the world to other cities, not 50 in one place.

"I went to bed knowing I'd sold 10 dates, and woke up to the news I was booked to do 50.'

Michael announced he was to perform a 10-night residency at a press conference in London on March 5, but after overwhelming demand for tickets, promoters AEG announced a further 20 shows on March 11, which was later increased to 50.

Sources close to Michael – who is believed to be undergoing treatment for skin cancer – are also said to be concerned about the 50-year-old pop star's weight, saying he is only eating once a day.

A source told Britain's The Sun newspaper: 'Michael has a phobia about getting fat. He doesn't want to put on any weight at all. It's not healthy for him because he weighs less than 126lbs now.

'But he is insistent that he'll only eat once a day and is adamant that's enough food for him. He's very thin and frail.'

'Thriller' singer Michael has already postponed the first four dates of his sell-out London shows, and his residency at the 20,000 capacity O2 area will now start on July 13.