Penn has been given the task of figuring out how to make his superhero film mesh with the upcoming Iron Man 2, Thor and Captain America movies slated for release prior to the Avengers's 2012 premiere, SciFiWire reports.
He admitted that he is daunted by the responsibility of bringing all the characters together on screen in a cohesive manner.
He said: "It's hard to make a good movie. We all have the best intentions, and it still might suck."
Penn added that he is meeting with writers of the other Marvel projects so that they can put together storylines which will overlap.
He explained: "They're doing Captain America and Thor first, and then Avengers is coming out.
"I'm taking a meeting next week with the Thor and Captain America people, and we are all going to get together, and I will see what is going to happen. I'll see where they are leaving the characters; it's pretty complicated.
"There's a board that is tracking what is happening. [We'll see] how this movie overlaps in that movie."
Penn previously wrote the screenplays for the last two X-Men movies.
Marvel recently announced that it has pushed back the release dates for all three in-development films.