Harrison, who was never arrested or charged, is being sued by Dwight Dixon for $100,000 in damages in a suit filed in Philadelphia on Sept. 2. Police are investigating the shooting, the District Attorney's office said Wednesday.
Dixon says he sustained "serious and permanent injuries" to his arm and body and a "severe shock" to his nervous system on April 28.
His lawsuit contends he was shot by Harrison and he was shot by someone using Harrison's gun. That approach covers both what Dixon says happened -- that Harrison pulled the trigger -- and Harrison's defense that someone else fired the player's gun.
Dixon's lawyer, Robert Gamburg, told The Associated Press that Harrison has admitted that his gun was used in the shooting, making the player liable because he was negligent in storing the weapon.
"If you own a gun, you're duty-bound to know where it is and if someone has taken your gun, which is basically what he is claiming, then he still is responsible for it, civilly," Gamburg said.
Calls to Harrison's attorney, Daniel Hart, and his agent, Tom Condon, were not immediately returned. In April, Condon denied the player was involved in the shooting.
Colts coach Tony Dungy said Wednesday the team has received no new information about the case for a few months.
In late April, Dixon and Harrison had a confrontation, Gamburg said.
"It apparently built up over time," the lawyer said. "I don't know if it actually came to blows, but certainly there were words exchanged."
Police said the shooting occurred near a North Philadelphia car wash owned by the All-Pro receiver that is about a half mile from a bar he also owns.
Harrison, who is from Philadelphia, has played all of his 12 seasons with the Colts and is the franchise's record-holder in every major receiving category. He is one of only four players in league history to top 1,000 receptions.