The former Bournemouth boss has been established as the clear leader of the post but no announcement has been made.
As the wait dragged on, Celtic admitted when launching their season ticket campaign that they had hoped to name the new manager before now.
And it is understood that talks with Howe have now completely collapsed nearly three months after Neil Lennon stepped down from his role.
The Englishman spoke with Celtic boss Dermot Desmond in London two months ago and was due to take over for the new season.
But the Premiership giants were forced to rethink by the news of the bomb Friday afternoon.
Previously linked bosses have already taken jobs elsewhere, with Jesse Marsch going to RB Leipzig and Enzo Maresca taking over from Parma.
And Celtic will now have to act quickly to appoint their new manager with the start of the season just a few weeks away.
New football manager Fergal Harkin is about to arrive, but the summer rebuild has now been significantly delayed.