Scarlett Johansson (WENN.COM file photo)

Scarlett Johansson is preparing to reunite with her Iron Man 2 co-star Robert Downey, Jr. after replacing Angelina Jolie in new sci-fi movie Gravity, according to a report.

The Wanted beauty was originally offered the role as director Alfonso Cuaron's leading lady in the upcoming 3D film, but she declined and now Johansson has "verbally agreed" to star.

The New York Daily News claims Downey, Jr. is slated to appear alongside the Lost In Translation actress in what Cuaron is allegedly touting as "the most ambitious film, technology-wise, since Avatar".

Sci-fi epic Avatar, directed by James Cameron, was lauded for its stunning 3D effects and won Oscars for Art Direction, Cinematography and Visual Effects at the Academy Awards earlier this year.

It also became the world's highest grossing film of all time after earning more than $2 billion at the global box office, beating the previous record of $1.8 billion set by Cameron's last smash hit, Titanic.