The Cats claimed within an official statement released on Wednesday afternoon that the dreadlocked Miers have succumbed to a syndesmosis strain in his left ankle.
After speaking with specialists over the course of the past week, it was confirmed that the dreadlocked 22-year-old would go under the knife ahead of Round 1.
“Gryan is an important player for us, as he has shown over the past three years,” General Manager of Football Simon Lloyd told geelongcats.com.au.
“We reviewed the scans and considered all possible options before determining that surgery was required. As we have seen with this type of injury, it is difficult to outline a return date, as everyone heals and rehabs differently.
"Gryan will undertake his rehabilitation diligently and professionally to get back on the field as soon as possible."
With many variables still at play, Geelong was unwilling to put a timeline on the local product's return to the field.
After trading Bunjil Bagora for Kardinia Park over the summer, former Hawk Ceglar was tipped to play a leading role at stoppages for the Hoops this season.
And while this will remain the plan for head coach Chris Scott, a non-descript "training mishap" forced the 30-year-old into receiving an arthroscopy on his right knee.
However, Lloyd held the view that Ceglar would "make a quick recovery".
The 101-gamer spent time on the sidelines last season with an ankle injury and ruptured his ACL during the Hawks' 2016 season.
Geelong parted with a future third-round selection to land Ceglar during the most recent trade period.