They’ll be joined by “August” cast members Julianne Nicholson, Juliette Lewis, Margo Martindale, Chris Cooper and Dermot Mulroney.
Clooney, a producer on the film, recently premiered the pic at the AFI Film Festival.
“As you well know, Julia (Roberts) is an alcoholic,” Clooney joked. “It was easier to work with her because you just offer her booze, apply that with anything.”
Co-starring Meryl Streep, the bigscreen adaptation of the Tony award-winning play opens Dec. 25 in U.S. theaters.