Board Thread:General Discussion/@comment-10266932-20130531151056/@comment-11051098-20130909132907

Well, he achieved Bankai through the guidance of Yhwach-Zangetsu, and since the old Zangetsu was not based on an Asauchi, it might have been more like a Spirit Weapon, of construction.

But he still achieved Bankai, and the real Zangetsu was shown to attain a Bankai as well, so I doubt he will have to achieve it over again.