"I was worried about how not playing regularly would affect my chances with Wales," said Duffy.
"I think the manager had already said, and not just about me but anyone, that if you're not playing week-in, week-out then you're not going to get in his side.
"That was a major factor in me saying yes when Swansea came in. I spoke to him about the move and he gave a good account of the club and what's going on there.
"And he assured me dropping down a league and playing in League One wouldn't be an issue. As long as that was the case it was all go and I was happy to sign."
Duffy will stay with the Swans until the end of the season.