The Vin Diesel Experience (he is quite a ride) reports that the muscle-bound star of "The Chronicles of Riddick" might be up for playing the opponent in the attempted restart of the "Rocky" franchise:

"Katzenberg is in talks with Sylvester Stallone to bring Rocky over to Dreamworks. The company is quite happy with what Sly's doing for 'The Contender' and are apparently dotting i's, crossing t's, to see that Balboa can safely set up shop at the Shrek stable.

Sylvester and Sage Stallone are apparently the duo negotiating the deal (both plan to star in the film, playing father and son). The only casting rumor thats surfaced is Vin Diesel playing the new opponent. I assume he'd be playing some kind of new hot shot, because the script reeportedly revolves around Balboa's big comeback and a new hot-shot that he has to bring back down to earth".

Thanks to 'Dan'.