Thanos seems to be the only thread connecting Earth’s Mightiest Heroes and the galaxy’s band of outlaws. Guardians of the Galaxy officially introduced Josh Brolin’s Thanos into the Marvel Cinematic Universe and eventually he will make his way to Earth, where The Avengers are going to have to stand against him and his quest to retrieve the six Infinity Stones. Though the characters may not know of Thanos’ existence, the actors playing them know that a showdown is coming. Jeremy Renner is fully aware but when pressed on the idea of The Avengers and the Guardians of the Galaxy teaming up in the future, he sounded less than optimistic.
Renner seemed to indicate that there were no plans to include the Guardians of the Galaxy in Avengers: Infinity War, saying that he assumed Marvel planned to give the Guardians another movie of their own, “and then we’ve got Infinity War I and II.”
Renner’s explanation does make sense. James Gunn has remained adamant that the Guardians will be occupying and exploring their own universe rather than bend to the whims of the Avengers so a crossover between the two teams does seem unlikely prior to Infinity Wars. Not to mention the Phase Three lineup is already set so a crossover is not happening anytime soon.