Dr Dao was left bloodied after law enforcement officials dragged him off the plane as he refused to leave the flight bound for Louisville, Kentucky.
The footage provoked international outrage and the Dao family issued a statement expressing gratitude for the “outpouring of support”.
Asked what the company would do in future if a seated passenger refused voluntarily to leave an overbooked plane, Mr Munoz said: “We’re not going to put a law enforcement official to take them off.”
He added that Dr Dao had not been at fault: “He was a paying passenger sitting on our seat in our aircraft and no one should be treated that way. Period.”
But on Monday Mr Munoz said Dr Dao’s conduct meant employees had been “left with no choice but to call Chicago Aviation Security Officers to assist in removing the customer from the flight”.
On Wednesday, two of the aviation security officers involved in removing Dr Dao from the plane were “placed on leave”, the Chicago Department of Aviation said, adding to one other that was suspended on Monday.
The US Department of Transportation is reviewing whether United complied with rules on overbooking.