In the DC Comics series Sinestro started out as Green Lantern Hal Jordan's mentor before becoming a super-villain - and Campbell warned fans not to expect any difference in his take on the story.
He told Superherohype.com: "I think it will stick closely to the origin story, but we all know Sinestro, for an example, is a character who goes over to the dark side, and of course, Carol, played by Blake Lively, in later versions becomes a bad guy as well.
"I think people will be able to see forward to the characters that in the comic went on to [become bad guys]... but people will be ahead of us on all that I think."
Actor Mark Strong is currently in negotiations to play Sinestro while Peter Sarsgaard is attached to star as villain Dr Hector Hammond.
Green Lantern, starring Ryan Reynolds, is expected to arrive in cinemas in June, 2011.