Miley Cyrus is making 'X Factor' bosses nervous ahead of her performance on the show tomorrow (17.11.13).

The 'Wrecking Ball' singer has reportedly been told to tone down her act for the family-friendly show after her controversial 'twerking' at the MTV Video Music Awards with hitmaker Robin Thicke.

A source told the Daily Star newspaper: ''Miley seems to be on a mission to be as controversial as possible so everyone's a bit nervous. She's been told to tone it down for The X Factor. That said, we're not stupid.''

Although big bosses don't want the performance to result in complaints, head judge Gary thinks 20-year-old should include her controversial rump-shaking move.

Earlier this week he said: ''It's music - she's a young girl. If that's the way she wants to express herself, fair enough. It's a tricky one because I remember Madonna when she brought her 'Sex' book out and everyone was going crazy. That seemed more shocking.

''But, you know, there's an off button. I always say, if you don't want to watch it, turn it off.''

He added: ''These singers are young, sexy girls - of course they are going to express themselves like that. But I don't let my kids watch it.

''I probably wouldn't let them watch anything like that, it's too sexual for them.''