British singer Amy Winehouse performs during the "Rock in Rio" music festival in Lisbon May 30, 2008. [Agencies]

Amy Winehouse briefly left hospital yesterday. The 'Rehab' singer - who was admitted to hospital after collapsing at her home last week - was allowed to attend a rehearsal for Nelson Mandela's 90th birthday concert in London's Hyde Park, where she is due to perform on Friday.

A source said: "Amy doesn't want to cancel - it's keeping her going. She begged the doctors to let her out to rehearse. "She went into the studio for a few hours and sang her heart out. She sounded amazing. No matter what else is happening in her life, Amy can still turn it on." Amy is also scheduled to perform at the Glastonbury music festival on Saturday.

Although Amy's dad, Mitch, recently voiced his fears she was suffering from emphysema, doctors are still trying to diagnose what is wrong with Amy.

A source said: "She has scarring on her lungs, which doctors say could lead to emphysema, but she isn't as bad as her dad first thought." Tracey Miller, Amy's US-based representative, has also denied she has the debilitating lung disease.

She said: "She is not diagnosed with full-blown emphysema, but instead has early signs of what could lead to emphysema."