The Ukrainian, who also holds the WBA, IBF, IBO and The Ring heavyweight championships, faces Leapai on April 26 in Oberhausen, Germany.
Leapai earned a shot at the belt after becoming the mandatory WBO challenger with a surprise win over Denis Boytsov last November.
Samoan-Australian Leapai heads into the fight ceding height and weight advantages to Klitschko, making him the underdog for the clash at the Konig-Pilsener-Arena.
But Klitschko is expecting his 16th title defence to be a challenging one.
"Maybe he's an underdog, maybe an underdog for this fight, but what we're going to see from Alex Leapai on the 26th of April is pure violence," Klitschko said.
"I think it's going to be challenging. As I said he has some downsides but also some really strong sides. It's going to be challenging for me because of the size difference and his desire to win.
"I could tell when I saw it at the press conference, he's determined and really wants to make it happen and I look forward to it and it's going to be an exciting night.
"It's not going to be boring. That fight is not going to be boring at all."
Klitschko also insisted that he is relishing the extra pressure on his shoulders following the retirement of older brother Vitali.
"Vitali retired recently. So now the whole focus is back on one of the Klitschko brothers," he added. "But I love this pressure, it's a certain weird pressure.
"I know how to handle it, I know what to do with it, it's a great motivation actually for me.
"In a certain way, I'm still fighting for two. We are sharing the same family name. It became a brand with different sides in it. I'm looking forward to achieving my goals and be challenged by the guys that are out there."