Vin Diesel is in negotiations to join the cast of Guardians of the Galaxy as Groot, according to Deadline.  The actor himself teased the role with a Facebook post of a photo of Groot on Sunday, which was taken down a few hours later.  No official word came from Marvel at its D23 presentation over the weekend.

Most of the cast of Guardians of the Galaxy was introduced to the fans for a photo at San Diego Comic-Con (see "Marvel Releases Cast Photo").