Now the court system could get involved in the United fiasco.

Dr. David Dao, who was dragged off a plane in Chicago last Sunday, isn't filing a lawsuit yet.

But his lawyers say he plans to. And they filed an emergency petition on Wednesday asking that all potential evidence from the episode be preserved.

"Will there be a lawsuit? Yeah, probably," Thomas Demetrio, Dao's attorney, told reporters Thursday. He said both United (UAL) and the Chicago authorities who manhandled his client could be liable.

Legal experts say Dao has a good case against both parties once he decides to file.

Related: Man dragged off United flight has concussion, will file suit, lawyer says

As everyone now knows, Dao was pulled off a plane, bloodied and screaming, at Chicago O'Hare International Airport. He had refused to give up his seat on a flight to Louisville, Kentucky. United needed to free up seats for commuting crew members.

Trial lawyer Aaron Podhurst, who represents plaintiffs in aviation cases, said he believes Dao can make a strong civil case based on the assault and battery that appears to have occurred. United could be liable, and Dao could also sue Chicago authorities for use of excessive force, Podhurst said.

"This case is a very strong case for the passenger," Podhurst said. He added that he expects Dao would be able to secure a settlement.

Passengers agree to a litany of terms in any airline's "contract of carriage," which they agree to when purchasing a ticket. But the agreement doesn't sign away the right to sue if the airline treats a passenger in a manner that breaches the law.

"If you're injured, or dragged off the airplane, or falsely arrested, you can sue," said Andrew Harakas, head of the aviation law group at Clyde & Co.

Related: How United could have avoided this fiasco

Airlines do have legal protection if they act in a reasonable way when refusing to transport a passenger that is a threat to himself or other passengers, Harakas said.

David Katzman, an aviation lawyer with Katzman Lampert & McClune, said that standard doesn't likely apply in the United case.

"You could give this to a group of first-year lawyers and they could list all the claims this guy has," he said, naming intentional infliction of emotional distress in addition to assault and battery.

United CEO Oscar Munoz initially said that Dao was "disruptive and belligerent." But on Wednesday, Munoz walked back such language, saying he did not blame Dao for what happened. He told ABC that United did not give its managers "the proper tools, policies, procedures."

United said Thursday that Munoz and the company have called Dao repeatedly to apologize.

"We cannot stress enough that we remain steadfast in our commitment to make this right," the company said.