The "Mamma Mia!" star felt sure the film would bomb even though James Gunn's script was "great", and now admits she was "very wrong."
"I didn't want to be part of the first Marvel movie that bombed," the actress tells The Hollywood Reporter's "Awards Chatter" podcast. "I said, 'Who wants to see a movie about a talking tree and a raccoon...?' I was very wrong."
The film went on to make over $770 million (£576 million) at the global box office.
"The script was great; it was all based in not wanting to be 'that guy,' " Amanda adds, "because if you are the star of a giant movie like that, and it bombs, Hollywood does not forgive you. I've seen that happen to people and it was a giant, giant fear and I thought, 'Is it worth it?' "
The role eventually went to Zoe Saldana.
After exploring the galaxy in two standalone movies, the Marvel ragtag team of misfits eventually joined The Avengers in "Avengers: Infinity War" and then returned for "Avengers: Endgame". Now a third "Guardians of the Galaxy" movie is currently in development as part of the Phase Four of the Marvel Cinematic Universe.