The 47-year-old actor starred as Leonidas in the hit 2006 action/adventure movie and in one particular scene, his character kicks a man down a pit while shouting "this is Sparta" and Gerald revealed while filming this now iconic scene, he suffered a hernia by the second kick.
Speaking to ShortList magazine, Butler said: "My whole psyche through filming was, 'This guy's been through hell, he's been through much more than I'm going through, so the least I can do is get a hernia from doing a little kick.' Which I pretty much had by the second kick. My hip flexor was gone, a hernia ... but it was cool."
The film follows the war between Persia and Greece and Leonidas leads an outnumbered warriors against the massive Persian army.
Although their certain death awaits the Spartans, their sacrifice inspires all of Greece to unite against their common enemy.
Butler's hernia isn't the only injury the actor has received while filming as his career nearly ended prematurely after an on-stage incident during a production of Shakespeare's 'Coriolanus'.
He recalled: "We were supposed to be these revolting citizens - not that they were disgusting they were in revolt, rebelling. So [the director] puts us all together and he gives us the script.
"At this stage we didn't need the chisels that we had- we had these wooden chisels that they're supposed to use as weapons — but we didn't know our lines, and it's very physical theatre so they wanted 12 guys running.