By Adrian Warren

World heavyweight boxing champion Wladimir Klitschko has had to hold Australian challenger Alex Leapai back after former world champion Shannon Briggs gatecrashed their media conference in Germany.

Klitschko, who defends his four titles against the Queenslander on Sunday Australian time, was in the middle of some introductory comments at the media conference in Dusseldorf when 42-year old Briggs stormed into the room.

He called out Klitschko and questioned the quality of his opponents, describing Leapai as a bum.

"I switched into Lionheart mode, I really wanted to fight him," Leapai told AAP.

"But Wladimir just told me 'our focus is our fight, just leave it at that' so I just left it at that."

When 42-year-old former WBO champion Briggs finally left the room, Klitschko said a fight with the American, made no sense.

Briggs recently emerged from a three-and-a-half year hiatus following a loss to Klitschko's brother Vitali, with two first round wins in eight days.

Instead he defended his decision to fight Leapai, whose credentials had been questioned by Briggs.

"I've dome my homework for the last eight weeks and I'm ready for the exam," Klitschko said.

"I know I'm going to have a great challenge on Saturday night.

"He's the Australian Rocky Balboa."

Leapai said he was looking forward to making history.

"It's something I've been dreaming about for years.

"I have an opportunity now to fulfill my dream."

Unbeaten in his last 19 fights over 10 years, Klitschko stressed he was still highly motivated despite his seeming domination of the heavyweight division.

"Trust me, I'm not bored at all," Klitschko said.

"I've never felt as good as I do now."

Leapai's trainer Noel Thornberry cheekily said he was looking forward to his man having a rematch with Klitschko after the Australian won his title.