His character Elijah left town at the end of third season episode 'All My Children', which aired on February 16.
However, according to Assignment X, the 36-year-old actor insisted that he has "not entirely" left the CW drama at a recent NBC Universal Summer Press Day.
Gillies recently signed up for a new role, appearing alongside Smallville's Erica Durance in forthcoming NBC medical drama Saving Hope.
"Fortunately we film at different times during the year," he explained. "I'm deeply indebted to what [The Vampire Diaries] has given me, but [Saving Hope] takes precedence."
The star went on to praise Vampire Diaries executive producers Julie Plec and Kevin Williamson.
"I'd do anything for them in a instant," he said. "[But] I can't speak about anything further on the show, or I probably will be fired."
The Vampire Diaries continues on Thursdays at 8/7c on The CW. In the UK, the series airs on ITV2.
> Vampire Diaries showrunner: 'I don't want Matt Davis to leave'
Watch a clip from the next Vampire Diaries below: