Alex Leapai is close to a deal to fight unified world heavyweight boxing champion Wladimir Klitschko for the world heavyweight title on April 26 in Germany.

'Lionheart' Leapai earned his shot at Klitschko's IBF, WBA, IBO and WBO belts when he ended the unbeaten run of Denis Boytsov over 10 rounds in Bamberg last November.

But the 34-year-old's training has been hampered by a calf injury picked up in the victory.

Despite his war wounds and underdog status, the Samoa-born slugger is confident of a win.

"Come the day we fight, once he feels what I've got, he's going to get knocked out, or he's going to jump out of the ring," he said.

And the sentiment was echoed by Noel Thornberry, who trains Leapai in the Queensland town of Gatton.

"If Alex goes out there and forces his will on this guy, he'll knock this guy out inside of six to eight rounds," Thornberry said.

A victory could pocket Leapai over $10 million, a big turnaround for a man who did not even pick up any purse when he beat Matt Hicks on the undercard to Sonny Bill Williams and Francois Botha.

He boasts an impressive 30-4-3 record with 24 knockouts in his 10-year career, but will face a living legend when he goes up against Klitschko.

The devastating Ukrainian's last win, a comfortable points decision over Alexander Povetkin to retain the World Boxing Association (WBA) crown, marked the 15th time he had defended his belt.

It also continued his outlandish undefeated run, which will pass 10 years shortly before the Leapai bout, to 61 bouts.

Klitschko, 37, sits third on the all-time list of consecutive heavyweight title defences - behind only legends Joe Louis (25) and Larry Holmes (20) - and second on the list of victories in heavyweight title fights - trailing Louis (26) and tied with Muhammad Ali (22).

He is also eyeing the winner of Bermane Stiverne and Chris Arreola, slated to take place around the same time as his fight with Leapai, for a shot at the WBC title vacated by his brother Vitali's decision to enter politics.