"Is he Groot?"

That's the new question at the core of Vin Diesel's mysterious dance with Marvel Studios. Rumors have swirled over the past several weeks about Diesel's involvement with Marvel -- most originating with the actor himself -- but now it appears we're close to an answer: It looks like Diesel might play Groot in director James Gunn's Guardians of the Galaxy.

The actor posted a photo of Groot on Facebook over the weekend, presented without a caption. It's curious timing, as Disney's D23 Expo was under way in Anaheim, California, but the even passed without Marvel making any additional casting announcements. However, following the image's appearance, Deadline's Dominic Patten rushed to report "I've learned" that Diesel is in negotiations for the role.

Perhaps Diesel's deal isn't signed in ink just yet — or perhaps the Fast and Furious star is just toying with his fans. After all, his earlier Marvel posts seemed to point in the direction of the part of the Vision in Avengers: Age of Ultron.