The heavyweight fighters are set to compete at the Oct. 24 pay-per-view event at a location to still be determined.
Sport.ru was the first to report the story.
In his last octagon appearance, Harris (13-8, 1 no-contest) lost to Alistair Overeem at UFC on ESPN 8 this past May in Jacksonville, Fla. It was Harris’ first fight since the death of stepdaughter Aniah Blanchard, who was the victim of a violent crime in the fall of 2019.
Volkov (31-8) was defeated via unanimous decision by Curtis Blaydes at UFC on ESPN 11 last month.