After curtains come down on the 13 participants on stage, they are hurried through passageways that lead them around the Las Vegas MGM resort. They leave the building and emerge again at the back of the theatre.
Mr Cox, a resident of Kent, fell while being led through these passages by stagehands. He was taken to hospital with a dislocated shoulder at the time.
He said doctors later diagnosed him with a brain lesion. Mr Cox's lawsuit claimed he has spent over $400,000 (£239,000) on medical bills, according to NBC News.
Benedict Morelli, Mr Cox's attorney, said in his opening statements that "there was a duty by the defendants to provide a safe environment to the audience participants".
When Mr Morelli asked Mr Copperfield whether or not a participant's injury was his fault, Mr Copperfield responded: "It would depend on what happened. If I did something wrong, it would be my fault."
Mr Cox alleges there was construction debris and dust in the passageways his client used, but Mr Copperfield said he walked the same path earlier and it was clear.
The Las Vegas resort MGM is also a defendant in the lawsuit, and claimed its passageways were clear.
The resort's attorney, Jerry Popovich, said: "Mr Cox did not slip; he tripped."
