United Airlines and the city of Chicago have agreed to preserve evidence related to the incident where a passenger was violently dragged off an overbooked flight, according to a lawyer.

Thomas Demetrio, attorney for the passenger David Dao, said on Saturday due to the agreement, a court hearing which was scheduled for next week will not take place, Xinhua news agency reported.

Dao, the 69-year-old Vietnamese American doctor was violently removed by aviation security officers from the United flight at Chicago's O'Hare International Airport to make room for its own crew members.

Dao suffered concussion, broke his nose, and lost two front teeth.

The video of this bloody incident went viral and sparked social media uproar, in which many echoed a call to boycott the airline.

Facing public outrage, United Airlines finally apologised and promised that this kind of incidents would never happen again.

However, it is not clear if the United would like to choose a settlement or go to court.

Chicago could also be sued, as the aviation security officers were hired by the city.