The 57-year-old, who played 'watcher' Rupert Giles for the entirety of the show's six-year run between 1997 and 2003, despaired at the exclusion of creator Joss Whedon from the project.
"[Joss] wasn't asked [to do the movie] - in fact, I think they went to great lengths not to ask him," he told E! Online. "It's a hideous idea.
"I think ultimately he had the idea when he was 19, took it around Hollywood and two people said, 'I'll make your movie'. They changed the original concept… I'm very glad they've done very well with it since, all power to them, but I don't think [you can take] someone's concept and say, 'Actually we're going to remake our concept of somebody else's concept'.
"It's nonsense. Not that I feel strongly about it," he joked.
Head previously described the notion of a Buffy reboot as "horrible" and likened the finished movie to "a car wreck".
His former Buffy co-stars Nicholas Brendon and Eliza Dushku have also criticised the project, but Whedon admitted last year to having "mixed emotions" about his absence.
"I don't love the idea of my creation in other hands," he confessed in November. "But I'm also well aware that many more hands than mine went into making that show what it was."
> Anthony Head teases NBC's 'Free Agents'
Watch Anthony Head discuss Buffy the Vampire Slayer with Digital Spy below: