We're just days away from the box office debut of "Avengers: Infinity War," so excitement is high right now. At one time, though, Anthony Mackie didn't have much confidence in the film.

Mackie appeared on "Good Morning America" Thursday to promote the superhero flick, and he gave the hosts a lot of interesting insight on what it was like to be a part of the star-studded MCU movie. The film packs in so many actors that many of them never got to see a full script, Mackie included. As he told the hosts of "GMA," the pages that he did get weren't enough to initially convince him that "Infinity War" would be any good.

"I got 25 pages, which was the final fight sequence, and I sent a long email like, 'This movie's going to be awful,'" he said.

Mackie expanded on why he thought that, listing some of the points he made in his email. Not only did he share that he didn't see how it could work, he said there was "no story." Additionally, he worried it would be "the longest fight sequence ever."

Luckily, Mackie soon received reassurance. He found out that his 25 pages were a small fraction of the massive script; in total, there were 250 other pages, he said.

Mackie's "GMA" appearance included several other high points, including his description of how his co-star Mark Ruffalo is "problems" and a new "Infinity War" clip. Watch below.

"Avengers: Infinity War" hits theaters April 23.