Kid Rock believes Justin Bieber will go off the rails.

The 42-year-old musician - whose real name is Robert James Ritchie - says fame will eventually take its toll on the 19-year-old singer and he will embrace the darker side of celebrity.

He told America's GQ magazine: ''It's just a matter of time before someone puts a huge line of cocaine in front of Bieber and he's going to be like, 'Yes! This is f**king awesome!' ''

The rocker also spoke out about Britney Spears, admitting he felt sorry for the 'Toxic' hitmaker.

He said: ''Poor girl. Turned into a space cadet. That dead stare, just f**king like someone stole her soul... ''

Kid isn't the only star who is worried about Justin, Channing Tatum recently revealed he thinks the 'Baby' hitmaker - who was discovered at the age of 14 - found fame too young and hopes he doesn't go off the rails like many child stars do.

He said: ''I do believe that whatever age you become famous, you end up staying that age.

''I worry about Bieber, man. That kid's wildly talented. I hope he doesn't fall down into the usual ways of young kids because it' so hard for someone to be responsible when they're not asked to be.

''We're not asked to do things ourselves. You have someone there with a coffee. 'You want food? I'll get you food.' ''