Wiig commented last week that she and writing partner Annie Mumolo "aren't working on" a follow-up to Bridesmaids, but it was reported that Universal is considering making the film without the actress.
McCarthy, who played the bawdy Megan in Bridesmaids, has now said that Wiig's return would be key to her signing for a Bridesmaids sequel.
"God, I wouldn't want to [return without Kristen]," the actress told E! Online. "I would never want to. I think it's a terrible idea."
McCarthy went on to admit that she's heard nothing official about the proposed Bridesmaids sequel.
"I don't [know] anything about it. But I know that nobody wants to do it unless it's great. If it is, I will show up wherever those ladies are," she added.
Last year, Jon Hamm expressed his belief that Wiig will not return for another Bridesmaids film.
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Watch a trailer for Bridesmaids below: