During the segment, Hemsworth, who was promoting his latest film "Thor: Ragnarok" on Kimmel's show, sits with the host at the desk and reveals that he brought Ruffalo and Waititi with him to the show.
Kimmel sends a camera crew backstage to the green room so that they are included in the interview - but throughout, an uninvited Damon decides to pop in and steal the spotlight, reports deadline.com.
From there, his presence just gets more inconvenient - and bigger before Kimmel cuts to an exclusive clip from the movie.
"Thor: Ragnarok", which also stars Cate Blanchett, Tessa Thompson, Tom Hiddleston, Idris Elba, Karl Urban and Anthony Hopkins, is the third standalone movie for the title superhero played by Hemsworth. It is releasing in India on November 3.