An ability named 'FeministWhorePurna' was found inside the code for the PC version of the game by users on Steam. It is thought to have been an early name for Purna's Gender Wars skill.
International brand manager Blazej Krakowaik said that the firm was "disturbed" by the find and will launch a full investigation.
"It obviously violates professional and ethical standards at Techland and should never have happened," he told Eurogamer. "We're investigating this right now and we'll issue a statement later.
"For now, I can only express my sincerest apologies for this incident and assure you that whoever acted so irresponsibly did not represent the views and opinions of Techland."
He added: "I'm equally sure that aside from the author of that unfortunate line of code, everyone at the office is as disturbed by this as you are."
Dead Island has seen blunders in its launch week, with a day-one patch that fixes 37 issues, while a developer build of the game was accidentally uploaded to Steam for the North American launch.
Dead Island will be released on Xbox 360, PlayStation 3 and PC across Europe tomorrow.
> Read our review of Dead Island
Watch the launch trailer for Dead Island below: