The ATP (Association of Tennis Professionals) world number one is to star as himself in Sylvester Stallone's action sequel after receiving a personal invite from producer Avi Lerner.
Djokovic has already flown into Bulgaria to film his role, reports Deadline.
Stallone is reprising his role as Barney Ross in Expendables 2, while Jason Statham, Bruce Willis, Arnold Schwarzenegger, Dolph Lundgren, Jet Li, Terry Crews and Randy Couture are also returning to the cast.
Jean-Claude Van Damme, Chuck Norris and Liam Hemsworth are new additions to the Expendables lineup.
The Expendables 2 was struck by tragedy in October when stuntman Kun Lieu died filming an explosion scene at reservoir Ognyanovo, 15 miles from Bulgaria's capital of Sofia.
Watch the Expendables trailer below: