In July, Magners hired Fold7 as its lead creative agency without a pitch. The brand had appointed Leith to the account in 2014 but the Scottish shop did not produce any work. Magners previously used The Red Brick Road.
PHD and Magners were unavailable for comment.
It is the latest bad news for Havas Media Group over the past two weeks.
On Tuesday, Ubisoft shifted its global media into Group M just four months after hiring Havas Media. Last week, Havas Media Group’s Arena was forced to resign its newly won Virgin Atlantic account after an objection from Emirates, a client of Havas Media.