Leorio had lost his match with Leroute. It was up to Killua to win his match, so they could pass this part of the Hunter’s exam. He was going against Johness the Dissector. A mass murderer. Leorio didn’t want Killua to go against him for his safety, Killua went anyways.

Johness: “That’s right. A battle to the death. Soon, I’ll tear your body apart.”

Little did he, or anyone know that Killua is a Zoldyck. Gon already knew though. Leorio, Tonpa and Kurapika were watching carefully.