Law enforcement officials dragged Dr Dao off a flight departing from Chicago for Louisville, Kentucky, because it was fully booked, and the airline wanted four passengers to make way for staff members.
The 69-year-old Vietnamese-American physician had refused to leave, saying he needed to go home to see his patients. He was then dragged down the aisle of the aircraft.
His lawyer later said that Dr Dao found the experience "more horrifying and harrowing than what he experienced when leaving Vietnam".

The ordeal led to demonstrations at Chicago's O'Hare International Airport and turned into a public relations disaster for United Airlines.

The situation escalated when a response from the airline's chief executive, Oscar Munoz, failed to mention any use of excessive force.
"This is an upsetting event to all of us here at United. I apologise for having to re-accommodate these customers," he said in a statement. He also said that Dr Dao was "disruptive and belligerent".
Days later Mr Munoz, who was facing calls to resign from online petitions that had received thousands of signatures, said he felt "shame and embarrassment" and vowed that it would never happen again.
The airline offered compensation to all customers on board last Sunday's United Flight 3411.