Earlier this week, the Anchorman star suggested that he would be joining the NBC sitcom "full-time" as Deangelo Vickers.
However, Lieberstein, who also plays Toby in the series, told Vulture that there is no truth to the rumour.
"Will was joking," he confirmed. "But he commits to his jokes so fully that we're hoping he's with us long term, just as a [comedy] bit that won't end."
Rainn Wilson (Dwight) recently claimed that Ferrell will only remain on the show for a short stint.
Actors previously rumoured to be replacing the departing Steve Carell include Ricky Gervais and Will Arnett, both of whom will appear in the show's seventh season finale.
Flights of the Conchords star Rhys Darby also confirmed that he was briefly in contention for the role.
The Office continues on Thursdays at 9/8c on NBC.
> The Office star 'misses Steve Carell'