Sylvester Stallone was seen exiting a hotel in Atlanta carrying a script and getting into a car… and the Daily News is saying this means he is in Guardians of the Galaxy 2. The Creed star was seen exiting the same hotel where the cast of the film are currently staying and the car he got into is the same car that usually picks up Chris Pratt. So the evidence, though circumstantial, is pretty good.
Marvel has not said anything about the rumor. We know that there is a role for Peter Quill's father in the film, a role that a lot of people speculate is the one Kurt Russell is playing, but that also has not been confirmed. Perhaps Stallone will play Papa Quill in a cameo….