Film bosses were planning to shoot a big-screen remake of the classic show with Brad Pitt and John Travolta in the lead roles, but the project was scrapped in 2010 when producers instead decided to revive the programme on TV with surviving members of the original cast.
Duffy, who plays Bobby Ewing in the show, reveals he was given a look at a draft script for the planned movie and was convinced any efforts to bring Dallas back were doomed to fail.
He tells news website The Hollywood Reporter, "I personally never thought that Dallas would resurrect itself again because I didn't think anybody knew how to do it. And it was proven to me on the few attempts that were made.
"The movie that was going to be done, I read that script, it was atrocious. It was just awful. And I just didn't think anybody understood it anymore, you know? So I thought, 'Well, they might talk about it but it's never going to happen'.
"Then we heard that TNT and Warners wanted to do it and I still thought, 'Well yeah, right, okay, let's see what it's like'. And then I read the script, and the script told me it can be done. It was a great script."
The new season of Dallas launches in the U.S. later this month (Jun12).