The pair have been confirmed to be negotiating for Warner Bros' boxing comedy, reports The Wrap.
Peter Segal (Anger Management, Tommy Boy) is in line to direct the movie, which is yet to officially receive the green light but is still said to be moving forward.
Stallone and De Niro will star as ageing rivals who return to the ring for one final fight.
The film was first announced in 2010, at which time Segal said that he was keen for the two actors to take the lead roles.
De Niro was recently cast in Malavita and will next be seen in Red Lights with Cillian Murphy.
Stallone will appear in The Expendables 2 later in the year.
Watch a trailer for The Expendables 2 below: