Previous spin-off 'Once Upon a Time in Wonderland' was deemed a failure, but the network remains open to similar future projects, reported Hollywood Life.
"Showrunners Adam Horowitz and Edward Kitsis are endlessly inventive. They have a glimpse in their eyes of stories they're going to spin for many years to come on Once, and maybe beyond it," Lee said.
"It certainly doesn't rule out their ability or our ability to build on 'Once'. In many ways, Once itself changes every season by bringing on new characters - think of the world of Hook, of Wicked, and now to have teased 'Frozen'," he added.