According to Bleeding Cool, "multiple sources" have indicated that the Batman project has already entered production.
The report went on to say that the film is likely to visually resemble DC and Warner Bros' All-Star Superman animation, and feature the return of several "veterans of Batman toons past" among its crew.
Written and drawn by Miller, The Dark Knight Returns ran for four issues in 1986. The story follows a middle-aged Bruce Wayne, who comes out of retirement to don the mantle of the bat once again.
An iconic splash page from the series depicting the Caped Crusader alongside the Carrie Kelly incarnation of Robin is expected to raise more than $100,000 (£62,000) when it goes on sale at an auction in May.
DC and Warner Bros previously confirmed that an animated film based on Miller's Batman: Year One is also in development. It is expected to be released ahead of the rumoured Dark Knight Returns.
The Dark Knight Returns animation is yet to be officially confirmed.