Singer Amy Winehouse has "traces" of the lung disease emphysema but is "responding brilliantly to treatment", her father has said.
Mitch Winehouse told BBC Radio 1 his daughter would recover "completely" as long as she stopped smoking.
The star has now been in hospital for a week, but her father said she would perform at the Glastonbury Festival and Nelson Mandela concert this weekend.
Emphysema is caused by lung damage and can start as mild breathlessness.
It eventually means the body does not get enough oxygen, leading to further breathing problems and possibly death.
"There's a small amount there which hasn't gone too far and it's completely repairable," Mr Winehouse said.
The 24-year-old fell ill last week after fainting at her London home.
"With patience, her lungs will recover completely and she's responding brilliantly to treatment - she's actually flourishing," Mr Winehouse said.
He added that doctors had given his daughter permission to perform at the weekend.
"She will be well enough - not could be - she's well enough to be at Glastonbury now," he said.
But Dr Keith Prowse, chairman of the British Lung Foundation, said emphysema was not curable.
"Once it's there, it's there - it is possible to have it and not be bothered by symptoms, but if you continued to smoke it would cause it to progress rapidly," he told the BBC.
"If Amy stops smoking, it's not going to interfere with her singing and she probably won't have any trouble from it."
But in the late stages of the disease, a singer would "struggle to find the breath to perform effectively", he said.
Emphysema kills 30,000 people in the UK every year and is caused by gradual damage to the structure of the lungs, which makes it harder to exhale.
Caused by gradual damage to the structure of the lungs
Sufferers find it hard to exhale
Lack of oxygen can lead to fatigue and weight loss
Smoking is the principal cause in the UK
Cannot be cured, although radical surgical methods have been tried with some success
Can leave sufferers housebound, reliant on oxygen supplies, and eventually contribute to death
It usually affects older people as it is due to cumulative damage over a long period, such as a lifetime of smoking.
Dr Prowse also said more young drug addicts were presenting with the condition.
"People are starting to use drugs much younger these days so it is present much earlier," he said.
"They are smoking cigarettes heavily anyway and we know some of the other things that damage the lungs - cannabis for example.
"But they're not eating a reasonable diet and have a lifestyle which predisposes damage."
In an interview with the Sunday Mirror, Mr Winehouse also called for his daughter's drug dealers and circle of drug addict pals to stay away from her.
"I'm saying to those drug dealers, and they know who they are, if they are supplying crack to Amy, then they've got to take responsibility," he said.
"I don't want her hanging out with her mates like Pete Doherty either. What hope does she have if people are taking drugs around her?"