Wales head coach Warren Gatland favours Welsh-based players for his squad.
Priestland, 28, says he is happy with the move despite the expected adverse impact on his Wales chances.
"I'm comfortable with my decision, but I think it will have a negative effect on my international career. It's something I'll have to live with," said Priestland.
Priestland came off the bench to earn Scarlets a last-gasp win away against bottom-side Zebre in the Pro12 on Saturday with the final kick of the match.
He says leaving the region will be difficult, particularly seeing former outside-half rival Stephen Jones returning to Parc y Scarlets as attack coach next season.
"I'm not going to lie, I would have loved to have worked with Steve [Stephen Jones]," said Priestland.
"I think he's a very knowledgeable man, especially about rugby and he's a great guy as well.
"It was a shame when I found out he was coming back, but I'd already made my decision and I've just got to stick with that."
Priestland believes former Wales and British Lions fly-half Jones is the right man to take over from Mark Jones.
"I'm sure Steve will do a great job with the Scarlets," he said.
"There's a lot of quality players down there and I'm sure he's the right man to sort of mould them and get the team playing they way I know that they can potentially.
"Hopefully Steve has a lot of success as a coach as he did as a player down there."
Scarlets fly-half Rhys Priestland says moving to English club Bath this summer may harm his Wales career.