The two actors were famed for their musclebound roles during their 1980s heyday but they were left mortified during their latest joint project when each pulled a calf muscle performing routine manoeuvres.
Stallone got the injury jumping off a ladder so he warned his pal to take care, prompting Schwarzenegger to decide to warm up first - but he then suffered the same ailment doing his stretching exercises.
The Terminator star tells British magazine Live, "Sly pulled his calf. He said to me, 'Be careful jumping down from that ladder, Arnold.' I said, 'Thanks for telling me; I'm going to warm up first.' So the next morning I'm warming up and I pull my calf muscle.
"So now we're both injured and the doctor comes and has to give us both cortisone shots. It would never have happened 20 years ago. We were like two idiots standing there. It was pitiful."
The incident was not the pair's first health woes - they underwent joint shoulder surgery last year (12) before starting work on The Tomb.