"It's going to be a challenge," the father-to-be, 29, says in the June/July issue of Details. "I guess that late at night, I'm not so much scared as thinking of it as a huge unknown."
Brady is expecting his first child this summer with actress Bridget Moynahan, 35 – with whom he split in December after three years together.
"I want to prepare for it the way I do everything else in my life," he tells Details. "I make lists. I make plans. But being a father is different. I think that people go into it and find out, holy s---, I have no control."
"People want to go out and travel around and meet cool people. I could just go live in Vermont, but is that what I really want?"
Brady, who often keeps low-profile, has been the center of media attention lately for dating Bündchen while facing fatherhood with his ex. "It doesn't affect anyone but me anyway," he says, "so why is it a big deal?"