If the deal comes through, DeGeneres would voice Dory, a blue tang fish who was suffering from short-term memory loss in the 2003 original film, the Hollywood Reporter said.
Writer-director Andrew Stanton, who scripted the 2003 film and co-directed it, is set to return for the follow-up.
Victoria Strouse is writing the script and Lindsey Collins is producing.
A 2016 release date is projected.
The original, which won the Academy award for best animated feature, is still the highest-grossing orignal Pixar movie, earning USD 868 million to date worldwide.
The original film is being re-released in theatres next month in 3D.
