The pair are the hot favourites of director Peter Segal and are currently in negotiation. "Stallone and De Niro are expected to come on board as they're both fans of the director and have both sent themselves up in comedies in recent years," said a source.
The comedy, which was first announced in 2010, will see the pair go head-to-head in the ultimate boxing face-off. Doug Ellin, creator of popular TV series "Entourage", has been chosen by Warner Bros to write the script. The movie is expected to begin filming next year.