The injury to the 6-foot-6 forward from Ohio State occurred during a Summer League game on July 11 against the Atlanta Hawks in Las Vegas.
The Pelicans said the procedure performed Monday was a right ACL reconstruction and that Liddell remains out indefinitely.
Drafted 41st overall, Liddell averaged 19.4 points and 7.9 rebounds with the Buckeyes last season.
It wasn't clear if he was going to make the Pelicans' regular-season roster because the team already had 15 players under contract for next season. But Liddell could have been a two-way player, also spending time with the Pelicans' G League affiliate in Birmingham.