Two new journal pages have been posted named "Zaun Amorphous Experiment - Development Log 001" These files are named "Zac Journal Teaser" just as the previous were called "Quinn journal teaser"
Update: Riot has now removed Zac from the image's URL path. and left the "Journal Teaser".
Also, from the mac release video, we saw a green slime, along with some broken glass, could this be him?
Update: As Zerglinator points out, the picture in the second journal looks very close to Grumpy Monkey's (Senior Character Artist) current Icon.
Update 2: kYwzor had a great find and noticed Grumpy Monkey's Icon is part of Battle Bunny Riven's splash art. This wouldn't be the first time Riot has put a sneaky spoiler into a splash art but it could also not be related, what do the viewers think?