The Ukrainian boxer announced his next fight on social media by posting the official fight poster.
“See you on August 26,” Usyk wrote.
Oleksandr Usyk, 36, successfully defended his titles last August, winning a split decision against Anthony Joshua.
Daniel Dubois, 25, won the WBA regular world title in June last year by a fourth-round knockout of American Trevor Bryan, and in December he successfully defended his belt by knocking out South African Kevin Leren in the third round.
The news came three and a half months after the team of Oleksandr Usyk refused to continue negotiations with the team of Tyson Fury, who owns the WBC heavyweight boxing world title.