knock the props out from under

knock the props (out) from under (someone or something)

1. To undermine, weaken, or destroy something. The stock market crash knocked the props out from under a huge number of investment firms across the nation. Tom knocked the props from under our proposal during the meeting.
2. To erode or undermine someone's self-confidence or sense of self-worth. Losing her job really knocked the props from under Sarah. I hope she comes out of this funk soon. Don't let the boss's comments knock the props out from under you. He's hard on everyone.
See also: knock, props
Farlex Dictionary of Idioms.

knock the props out from under someone

Fig. to destroy someone's emotional, financial, or moral underpinnings; to destroy someone's confidence. When you told Sally that she was due to be fired, you really knocked the props out from under her.
See also: knock, out, props
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • knock the props (out) from under (someone or something)
  • knock the bottom out
  • knock the bottom out of
  • knock the bottom out of (someone or something)
  • rip the heart out of (something)
  • rip/tear the heart out of something
  • tear the heart out of (something)
  • burn down
  • burn someone down
  • give props to (one)