Sylvester Stallone has added a sporty edge to his upcoming Expendables sequel by casting tennis ace Novak Djokovic in the film.

The actor has teamed up with his fellow movie musclemen Arnold Schwarzenegger, Chuck Norris and Bruce Willis for The Expendables 2, the follow-up to his 2010 action film.

Stallone is currently shooting scenes in Bulgaria - and he invited world number one tennis player Djokovic to join him for a cameo role.

Serbian star Djokovic headed to a warehouse in Sofia on Tuesday and spent a day filming his scenes for the movie with Stallone.