"I'm in preparation for a very incredible role," the heartthrob revealed to UK's BBC News.
Apparently, Usher has already started an intense fitness regimen to whip into shape for his new gig. "If you guys see me running around London, that's what it is."
Leonard, a world champion in five different weight divisions and Olympic gold medalist, finally retired from boxing in 1997 after a number of comebacks. He was named "Boxer of the Decade" for the 1980's.
Usher will have his hands full as he works on new music this year, too. "I'm doing [the film] while working on this album," he said.