Usyk became the undisputed champion with the WBC, WBA, WBO and IBF titles after defeating Tyson Fury on points.
He has now announced he will relinquish his IBF belt ahead of a bout between Joshua and Dubois at Wembley Stadium on September 21.
The Ukrainian boxer revealed the news via his Instagram account.
Dubois, who Usyk defeated last year, holds an IBF Interim belt. He would have been the mandatory challenger for Usyk, who is contracted to rematch Fury, a fight which has been fixed for December of this year.