The filmmaker told the New York Daily News that the heroine was originally part of the titular superhero team's roster, only to be dropped in favour of Scarlett Johansson's Black Widow.
"Trying to figure out the way you want to introduce all those characters, that was stuff we were still tweaking in the edit," said Whedon.
Wasp was a founder member of the Avengers in the Marvel Comics series, along with another character omitted from the movie, Ant-Man. Both heroes could make their cinematic debut in Edgar Wright's long-rumoured Ant-Man movie.
Desperate Housewives star Eva Longoria was once linked with the role of Wasp following reports that she was spotted leaving Marvel's offices. It later transpired that she held a meeting with studio executives about a different project.
The Avengers landed in UK cinemas on April 26, opening to £2.4 million in the territory. It will be released in the US on May 4.
> Read Digital Spy's review of 'The Avengers'
Photo gallery - The Avengers from comic to screen: