Gleeson said he is terrified of accidentally revealing the spoilers of the J J Abram's film, whose plot is kept under wraps, reported the Huffington Post.
"I become sick in my mouth when people talk about Star Wars," he joked, adding, "I'm so nervous I'm going to give something away."
Gleeson is a part of an ensemble cast along with Harrison Ford, John Boyega, Adam Driver, Andy Serkis and Oscar winner Lupita Nyong'o.
The 31-year-old actor went on to explain that there are legal restrictions that make revealing spoilers a dangerous proposition.
"It says you're allowed to say you're excited to be in the movie. That's it. That is literally all you're supposed to talk about," he added.
'Star Wars Episode VII' opens on December 18, 2015.