The follow-up to his 2006 Image Comics miniseries and its 2008 sequel will not debut in 2012 as originally planned.
"We were holding back from mentioning it, in hope we'd be able to make a better prediction of when the story will drop," the writer said on the series' website.
"But, due to a variety of other things, we still don't know. We're pretty sure it'll be 2013. I'll be highly surprised if it's in the first half.
"What happened? Basically, life happened. 'Scheduling issues' and all that. Sorry we can't be more specific. And we're sorry we announced it as early as we did."
Gillen previewed some artwork for the delayed series.
He also pointed out that he will reunite with Phonogram co-creator Jamie McKelvie on a story for the Marvel NOW! Point One anthology.
A teaser has been released by Marvel Comics for their contribution which shows Miss America Chavez - introduced in Joe Casey's Vengeance - punching Kid Loki.
Marvel NOW! Point One will arrive in November.