The man who was dragged screaming and bloodied from a United Airlines plane in Chicago is taking legal action against the airline.

Lawyers acting for Dr David Dao have filed an emergency request with an Illinois court requiring the carrier to preserve video footage and other evidence relating to the incident, which sparked outrage on social media.

Citing a risk of “serious prejudice” to their client, lawyers want United and the City of Chicago, which runs O’Hare International Airport, to ensure passenger and crew lists, cockpit voice recordings, surveillance footage, internal memos and all other materials related to flight 3411 are not destroyed.

Dr Dao, 69, was forcibly ejected by security staff from the overbooked flight to Louisville, Kentucky to make room for cabin crew.

United Chief Executive Officer Oscar Munoz eventually issued Dr Dao a full apology and said the company would no longer use law enforcement officers to remove passengers from overbooked flights following global outrage over the way Dr Dao was treated by airline and airport security staff.

But this has not stopped Dr Dao from hiring two prominent Chicago lawyers to represent him, engaging the services of corporate law specialist Stephen Golan and personal injury specialist Thomas Demetrio.

Paul Callan, a civil and criminal trial lawyer in New York, said the public outcry over Dr Dao's treatment is likely to push the airline to a quick and generous settlement.

“Because United has such a catastrophic PR problem, this case has a much greater value than such a case would normally have,” he said.

The family’s lawyer issued a statement saying Dr Dao is still recovering in a Chicago hospital, telling WKLY: “The family of Dr. Dao wants the world to know that they are very appreciative of the outpouring of prayers, concern and support they have received. Currently, they are focused only on Dr Dao's medical care and treatment.”

Footage from the incident shows Dr Dao, bloodied and dishevelled, returning to the cabin and repeating: “Just kill me. Kill me,” and “I have to go home.”

United Airlines issued three statements on the incident, at first suggesting Dr Dao was partly responsible and labelling him “disruptive and belligerent” in a leaked email.

On Wednesday, United said it would compensate all passengers on board the flight the cost of their tickets and would examine how it compensates customers who volunteer to give up seats on overbooked planes, adding that it would likely not demand that seated passengers surrender their places.

Some politicians in the US have called for new rules that could make it more difficult for airlines to overbook flights as a way of increasing revenue.

President Donald Trump said it was “horrible” that Dr Dao was dragged off the flight, according to an interview from the Wall Street Journal.

Mr Trump said that rather than ending the practice of overbooking, there should be no upper limit to incentives carriers can offer passengers in exchange for their seats on overbooked flights.

But Delta Air Lines CEO Ed Bastian defended overbooking as “a valid business practice” that does not require Government oversight.

“It's not a question, in my opinion, as to whether you overbook. It's how you manage an overbook situation.”