Zoro's upcoming opponent in Elbaf is likely to be Gunko, a Holy Knight.

Roronoa Zoro Is the swordsman of the Straw Hat Pirates ... This power was way too great for him to face at that point, and Zoro has only brought it out on rare occasions in the story.

One Piece is available to read via Viz Media. The series can be read by the fans officially and for free on the Shonen Jump ...