Fight scenes in Sylvester Stallone's new movie were so realistic that he broke his neck during filming, the actor says in a magazine interview.

Stallone stars in The Expendables, which boasts some of the acting world's best-known tough guys, including Arnold Schwarzenegger, Bruce Willis, Dolph Lundgren, Mickey Rourke and British actor Jason Statham.

The 63-year-old said a fight scene with the wrestling star Stone Cold Steve Austin became so "vicious" that he needed an operation for a hairline fracture and had a metal plate inserted in his neck.

Stallone, a writer and director on the film, told this month's FHM Magazine: "Man, it was seven guys, kicking each other's ass, one guy tougher than the next … no joke, our stunt guys were begging for mercy," he said.

"Actually, my fight with Stone Cold Steve Austin was so vicious that I ended up getting a hairline fracture in my neck. I'm not joking. I haven't told anyone this, but I had to have a very serious operation afterwards. I now have a metal plate in my neck."

The film centres around a team of mercenaries who embark on a mission to overthrow a dictator. It also features actress Brittany Murphy, who died last monthafter collapsing at home.

Stallone previously starred with Lundgren in Rocky IV – when he suffered similar injuries. He said: "Dolph Lundgren and I always went for it.

"I gave him orders to try to knock me out while the cameras were rolling. At one point, he hit me so hard on the top of the head I felt my spine compress." "He then hit me with an almighty uppercut. That night my chest and heart started to swell, and I had to be helicopter-ambulanced from my hotel to a nearby emergency room.

"I was told that Dolph had punched my rib cage into my chest, compressing my heart.

"If it had swollen any more, I would have died. After that, I was like, 'Dolph, it's only a movie, bro..."'