Kun Liu, 25, was shooting a scene near the Ognyanovo Reservoir in Bulgaria last October when he was killed in an explosion, reported Daily Express.
"The stunt team took it very, very hard and shut down for quite a while. It's happened twice before on films I've been on and it's never easy," he said.
Liu's parents are suing the film's producers for more than 15.6 million pounds, claiming movie executives failed to take proper safety precautions on the set.
It's not the only tragedy Stallone, 66, is dealing with at present. His 36-year-old son Sage was found dead in his Hollywood Hills apartment last month, forcing the movie star-director to miss a series of promotional commitments for "The Expendables 2".
Meanwhile, his half-sister Toni Ann Filiti's lung cancer battle has taken a turn for the worse and she has been admitted to a Los Angeles hospital in a critical condition.