Trent Reznor. (AP File)

Rocker Trent Reznor has hit out at former pal and music protege Marilyn Manson, dubbing him a "dopey clown" and accusing him of allowing booze to wreck his career.

The Nine Inch Nails frontman first spotted Manson, produced his debut album and took him on tour with his band back in the mid 1990s.

He claims the shock rocker was dedicated and driven, but has allowed drink and drugs to take over his life.

Reznor tells Spinner, "He is a malicious guy and will step on anybody's face to succeed and cross any line of decency. Seeing him now, drugs and alcohol now rule his life and he's become a dopey clown. He used to be the smartest guy in the room. And as a fan of his talents, I hope he gets his s**t together.

"During the (Downward) Spiral tour (1994-95) we propped them up to get our audience turned on to them and at that time a lot of the people in my circle were pretty far down the road as alcoholics. Not Manson. His drive for success and self-preservation was so high, he pretended to be f**ked up a lot when he wasn't."