(Cover) - EN Showbiz - Amy Winehouse won't appear on stage again "for years", it has been claimed.

The troubled British singer, who has battled problems with drugs and alcohol, was booed at a gig in Serbia on the first night of her 12-date European tour over the weekend. It has been alleged that despite a ban on alcohol during her tour, Amy managed to sneak some drinks backstage in Belgrade.

She was an hour late for the concert and then proceeded to slur her words, drop the microphone, miss her cues and looked confused as she walked unsteadily around the stage.

The 27-year-old star's manager Ray Cosbert has now reportedly decided that Amy should retire "indefinitely" until she cleans up her life.

"It has been hard for Ray to watch her get into trouble over the years," a source told British newspaper The Sun. "There's only so much he can do - but enough's enough. She's going away and this time it could be for years."

After her shaky performance in Serbia, Amy's management team cancelled shows in Turkey and Greece which were scheduled for this week.

"Despite feeling sure that she wanted to fulfil these commitments, she has agreed with management that she cannot perform to the best of her ability and will return home," a statement read. "She would like to apologise to fans expecting to see her at the shows but feels that this is the right thing to do."

The remaining 11 dates on Amy's European tour have also reportedly been cancelled and those close to her believe she should enter a lengthy rehab programme.

Before her series of shows kicked off, Amy spent a week at The Priory clinic in London, with her representative explaining she had "embarked on a treatment programme" to ensure she was ready for performances in Europe this summer.

The singer famously previously stayed at The Priory on occasions between 2007 and 2009. (C) Cover Media