CHICAGO - A lawyer for a man who suffered a concussion and lost two teeth when he was dragged off a United Express flight hopes the 69-year-old becomes "a poster child" for the mistreatment passengers suffer at the hands of the airline industry.

Attorney Thomas Demetrio indicated Thursday Dr. David Dao will sue United and the city of Chicago, which employs the officers who pulled Dao off Sunday's Louisville-bound flight.

In widely shared cellphone video, Dao is dragged down the aisle on his back, his face bloody.

Demetrio said the video showed an extraordinary instance of something that happens too routinely: Airlines overbooking flights then bumping paying customers.

He says it exposed a culture in which airlines have "bullied" passengers.

United has apologized and says it won't happen again.