Rumors of a movie based on the hit period drama, in which Coyle plays valet Mr. Bates, have recently circulated.
"If it's a great, great script, [I'd do it]," said Coyle during a recent press call for his new Sky1 drama Starlings. "You'd have to regard it on its own merit at the time.
"It's a good idea. [Julian Fellowes] is a terrific writer, so it would have to be something, I imagine, completely removed from the series."
Coyle admitted that he has no clue what has led Downton to become a "cultural phenomenon".
"I don't know what tipped it over," he said. "Nobody does. There's always theories that in times of austerity we look to nostalgia for comfort. There's all those social theories.
"There's [also] something about the open-ended, rolling nature of the story lines. You don't know what is going to happen, it's not finite in the same way a classic novel is, so... you get engaged in it in a different way."
Downton Abbey star Hugh Bonneville (Robert Crawley) has dismissed speculation that a film version is currently in the works.
"Julian Fellowes was at the Golden Globes and was... in conversation with people who work in films," he explained. "But to deduce from that that there is going to be a movie is a step too far. We'll have to do series three first and see what happens."
Coyle will next be seen in Sky1's Starlings which begins on Sunday (May 13) at 8pm.
Downton Abbey airs on ITV1 in the UK and on PBS in the US.
> Dame Maggie Smith leaving Downton Abbey?
Watch the cast of Downton Abbey discuss the proposed movie below: