In an update on the PlayStation Blog, Sony Computer Entertainment Worldwide Studios President Shuhei Yoshida explained that extra time was needed to fix bugs.
"The Last Guardian development team is fast approaching major milestones in production and has made the tough decision to delay the release of The Last Guardian a few weeks," he said.
"A delay is a difficult decision, particularly with this game, but we have encountered more bugs than anticipated while in the final stages of development. To ensure that The Last Guardian delivers on the experience that the game's creators have envisioned, we need to take the extra time to work on those issues."
He added: "Fumito Ueda (GenDesign) and Japan Studio have a wonderful vision for The Last Guardian's touching, emotional journey of friendship and trust, and we want to deliver the most polished experience possible for our fans who have supported us for so long."
Following years of silence from its developers and speculation that the project had been quietly cancelled, Sony announced development of The Last Guardian had shifted to PS4 at E3 2015. The game was originally revealed in 2009 as a PS3 title.
In November 2015, Sony said it was purposefully holding back what it shows of The Last Guardian because it is a story-heavy game. GameSpot played The Last Guardian at E3 2015; you can read Scott Butterworth's impressions here.