The New Orleans Times-Picayune said the actors were to play small roles in the film, but, as of this week, are no longer attached to the project, which is being shot in New Orleans through June.
Cohen said on Howard Stern's satellite radio show the "Django" shooting conflicted with his publicity duties for his movie, "The Dictator."
No reason has been reported for Russell's exit, the Times-Picayune said.
Tarantino's other films include "Reservoir Dogs," "Pulp Fiction," "Jackie Brown," "Kill Bill" and "Inglourious Basterds."
'Maze Runner' tops the North American box office
'Maze Runner' brings in $11.3M Friday