The actual modern Greek form of Blasius (see Blaise) is Vlasios (Βλάσιος). Vlasis is a diminutive of Vlasios.Further, I would like to note that Vlasios can also come from an authentic Greek name. For that, I refer to my entries for Vlasios and Blasios in the Submitted Names Database. :) Also check out this post of Pavlos at the Names Facts message board:Http://www.behindthename.com/bb/fact/16482Plus take a look at this section of Pavlos' website:Http://web.archive.org/web/20120324121302/http://www.etymologica.com/page3.htm.
https://el.wiktionary.org/wiki/%CE%92%CE%BB%CE%AC%CF%83%CE%B7%CF%82