Madonna looked a shadow of her usual self as she was snapped leaving a New York Kabbalah centre at the weekend.

Bereft of make up, the superstar singer looked pale, tired and gaunt, and her short-sleeved T-shirt revealed her grotesquely bulging, veiny arms.

The pictures have prompted speculation that the stress caused by recent media scrutiny over her marriage to Guy Ritchie, coupled with the release of her brother Christopher's tell-all book, is taking its toll on her looks.

Others, however, point to the 49-year-old's aggressive efforts to defy the ageing process through strenuous workouts, extreme dieting and plastic surgery as being behind her less than healthy appearance.

Harley Street plastic surgeon Angelica Kavouni, as quoted by the Daily Mail, says, "In my opinion, it is likely she has had filler in her cheeks because they are so full. There is no loose skin at the jawline which is also extremely unusual for someone her age. Typically, that is something we achieve through a lower facelift.

"Nor does she have any loose skin around her eyes, which again is unusual.

"She always had nice eyes and high cheekbones, so if anything has been done I think she's trying to enhance her existing good parts and had some areas tightened."

A source close to Madonna claimed earlier this year, "She's been having work done since her 30s, but in the past year she's really stepped it up, which is worrying."

Click to see Madonna's Changing Face