The French driver had qualified ninth in Saturday's session, and the stewards' decision promoted Alpine's Pierre Gasly to his compatriot's slot with Audi's Nico Hulkenberg moving up to 10th.
Hadjar's car failed a post-qualifying measurement inspection with a small section of the floorboard protruding millimetres beyond the limit in what Red Bull admitted was an error on their part.
"We made a mistake, and we respect the decision of the stewards," said team boss Laurent Mekies.
"No performance advantage was intended nor gained from this error."
The race start has been brought forward by three hours after weather forecasts predicted thunderstorms and lightning in the area of the Hard Rock Stadium. Mercedes' Kimi Antonelli starts on pole for the third race in a row.