The report says O'Neill, 74, missed part of the build-up during the week. That does not automatically change team selection or approach, but it does affect preparation.
At clubs challenging near the top, that kind of clarity is often enough to steady the week.
A trip to Kilmarnock is rarely treated as routine. Away matches in the Scottish Premiership can become physical, direct and uncomfortable if the visiting side is even slightly off its usual level.
For Celtic, the key now is avoiding emotional drift. A health concern around a manager can unite a dressing room, but it can also become a distraction if the performance starts untidily. The smartest response is usually the most basic one: control possession, manage the tempo and remove the sense of chaos from the contest.
This is where leadership inside the squad becomes important.
The update appears encouraging, and that should help settle nerves around the club. The next point to watch is whether Celtic can turn that reassurance into a composed display at Kilmarnock on Sunday, with attention then shifting back to the wider title pace and the manager’s full return to normal duties.