George Russell (26) will start Sunday's US Grand Prix from the pitlane after Mercedes worked on his car overnight to repair damage from a crash in qualifying, the Formula 1 team said.
The Briton qualified sixth, despite the crash in the dying seconds of the session, with seven-time world champion team mate Lewis Hamilton 19th on the grid.
Hamilton is now set to start 17th after Russell's demotion and an engine penalty for RB's Liam Lawson, who qualified 15th on Saturday.
Mercedes had brought a major car upgrade to Austin but said Russell would revert to the previous specification used in Singapore.
Mercedes scored points in Saturday's sprint race with Russell fifth and Hamilton sixth.