"He looked really, really stressed – as if he was really frightened," notes one concert-goer, from his last concert.

Says another, "He was out of control, touching up the backing singers and making a pass at the keyboard player. You could see it all on the big screen."

Robbie himself admitted not everything was right, telling the 65,000 fans he "felt like s**t".

"He seemed half a step slower and a little more bloated than his usual self," says another fan.

Soon after, his management confirmed Robbie was canceling part of the tour, revealing that continuing would "seriously impact his health". Insiders are now wondering if the former alcoholic and drug user has had a relapse.

Although he has been sober for six years, Robbie recently admitted he misses drugs.

"I'm still addicted to everything," he says. "I hate drugs, I love drugs. They haven't invented a new one that's not bad for you or less depressing than ecstasy, or one that makes you less paranoid than coke.

"As depressing and heartbreaking as it is, as soul-destroying and relationship destroying as it is, it makes life f**king interesting."