Reps for Disney, Lucasfilm and Harrelson have not responded to TheWrap's requests for comment.
Kathleen Kennedy and Allison Shearmur are producing the spinoff film, which is expected to begin production in January with Ehrenreich stepping into the Millennium Falcon in a role that Harrison Ford originated.
The film is slated to hit theaters on May 25, 2018. Harrelson and Shearmur have close ties from their previous work on "The Hunger Games," when Shearmur oversaw the project for Lionsgate.
The first "Star Wars Story," "Rogue One," has grossed more than $788 million worldwide since opening last month.
Harrelson next appears in "The Glass Castle" opposite Brie Larson, "Wilson," and the highly anticipated "War of the Planet of the Apes," in which he plays the new villain. He is repped by CAA.
Variety first reported the news of Harrelson's involvement.