The 20-year-old Irishman, a graduate of the Leicester City Academy, has already enjoyed two successful spells with Rovers since turning pro with the Foxes in 2010.
He spent five months at the Memorial Stadium between January and May 2011, making six appearances, before heading back to the West Country for the whole of last season, where played a further 42 times.
Cian was this week placed on standby for the Republic of Ireland Under-21 squad ahead of their away trips to Hungary and Italy during the forthcoming international break.