Board Thread:General Discussion/@comment-4041418-20140315151044/@comment-8669536-20140316105221

Never confirmed has far has i know. But the one/all we know for sure of are roughly human-sized. He could be the exception.

Well, according to Hitsugaya the Vasto Lordes are all small, approximately human-sized. (Chapter 197, page 16) If we assume Hitsugaya is right about this. And since the released state is supposed to reflect the earlier appearance of the Hollow, it is very unlikely that Yammy was a Vasto Lorde