It's an uncomfortable question. O'Neill is a popular figure among Celtic fans, and rightly so.
It's also important to note that we have defended O'Neill repeatedly on the basis of Celtic failing to properly prepare for this season. They haven't given him the tools he needed to succeed, and even the right tools that were added, they were added too late in most cases.
But this is a results-based business. O'Neill's job is to find solutions even when there are problems that were not created by him, and it won't be the board who lose their jobs due to poor form, it will be O'Neill.
So, let's cut to the chase - When will O'Neill be sacked, and when should Celtic consider making a decision?
We are now at a point where certain things cannot be ignored. Celtic cannot ignore that O'Neill has been unable to prepare his men for big occasions this season. They lack courage and conviction in big games, and they have even lacked fight in two of the three big occasions they have played in this season, which are the LASK, Rangers and Ferencvaros games.
Beyond that, teams are able to get on top of Celtic, and O'Neill is seemingly unable to stem the tide. It feels like they are hoping for the best, hoping that things turn around, while other managers would constantly be making tactical changes in a bid to find solutions.
Celtic have an ongoing midfield issue that O'Neill can't seem to find an answer for, and he has made some strange decisions, like putting Sam Johnstone in goal for the Old Firm.
What we need to see is O'Neill actively trying to affect games. He needs to prepare his men in a way that they are ready to go to war for the club, and he needs to be making more active changes to drop out of form players in a more ruthless manner.
At the moment, it's a passive approach, or at least it feels like one.
Celtic face Rangers again on Sunday, and if they come out of that one with a home defeat, making it back-to-back Old Firm defeats with four defeats in four big occasions, conversations are going to have to be had.
The extended international break will also give Celtic the chance to find a manager and allow him to work with the players before their October return to action, and that window is likely going to prove too tempting for the Celtic board, who are in danger of seeing this team slide, at least in terms of overall progress.
Let's hope that doesn't happen. No one wants O'Neill's Celtic return to end in a negative way. But there is no doubt that the pressure is on the veteran boss this weekend, and at the very least, conversations are going to be had if the Hoops lose again, and especially if they are as passive as they were last weekend.
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