Troubled star Amy Winehouse has confirmed she will sing at Nelson Mandela's 90th birthday concert on Friday - despite being diagnosed with early stages of emphysema.

The 24-year-old was released from hospital on Monday after doctors confirmed she has scarring of the lungs which can cause emphysema, but it is treatable.

Now the singer has pledged to honour her live commitments at both Glastonbury and the Mandela concert and has spent an hour-and-a-half in rehearsals since leaving the London clinic.

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Back on stage: Amy is back in rehearsals and confirmed she will perform at both the Mandela concert AND Glastonbury

A source told The Daily Star: 'Amy spent an hour-and-a-half rehearsing with her band on Monday night.

'She got through the best of her Back to Black album. She had been released from hospital for the rehearsals and although she didn't sing for the whole time she soundchecked and sorted out arrangements for the show.'

Low note: Shirley Bassey has pulled out of the Nelson Mandela concert

Nurse and medics will accompany Amy to the 4664 Mandela gig at London's Hyde Park and she will be whisked back to the hospital afterwards.

An offer of a helicopter to fly her in and out of Glastonbury to assure her the minimum of stress has also been put in place.

The Mandela concert was in crisis after it was revealed that both Dame Shirley Bassey and Amy were set to be no-shows.

Dame Shirley has been advised by doctors not to travel following her emergency stomach operation, her spokesman said.

The 71-year-old singer, who lives in Monaco, had been expected to recover in time for Friday's event.

Her spokesman Paul Carey said: 'The dame is hugely disappointed and was looking forward to the show immensely.'

Dame Shirley was rushed to hospital with abdominal pains in the middle of the night in May.

The Welsh-born singer underwent an emergency operation for stomach complications.

Dame Shirley, who wowed audiences at last year's Glastonbury festival, was said to be making a 'good recovery' and was discharged from hospital days later.

Queen, Leona Lewis, Annie Lennox, Simple Minds, Razorlight and the Soweto Gospel Choir are among the acts that will appear at Friday's concert.

Organisers have promised further stars on the bill, with 'several major artists keeping silent about their involvement in order to take both Mr Mandela and the audience by surprise'.

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Arrival: Nelson Mandela, with wife Graca Machel, who turns 90 on July 18th, at London's Dorchester Hotel last week