I wondered a few weeks ago on these pages whether 'Saint' Martin O'Neill, as some supporters dub him, had any more wonders left to perform.
It was after one of his former charges from the Seville glory days, Stiliyan Petrov, suggested the 74-year-old was working "miracles" by keeping the current squad in title contention.
Having just about kept the car on the road with last-gasp winners against clubs in the bottom four, the wheels then came off spectacularly in four portentous days in February. Back-to-back home defeats against Stuttgart and Hibernian in which six goals were conceded.
Surely the unlikely O'Neill fairytale was ending? Celtic couldn't go on the road to Baden-Wurttemberg, Ibrox and Pittodrie and emerge unscathed, could they?
Two victories and a draw later, there is a distinct air of renewed hope around the Scottish champions for the denouement to a season peppered with self-inflicted chaos.
A league and Scottish Cup double is still on the cards despite the departure of Brendan Rodgers, the sacking of Wilfried Nancy and woeful failures of at least two transfer windows.
O'Neill already has a Uefa Cup runners-up medal, three Scottish titles, three Scottish Cups and League Cup from his initial tenure over 20 years ago. Would this Premiership crown, were he to reel in Hearts, be his crowning glory above them all?
It's hard to top a European final, granted. However, right now there is no Henrik Larsson thrashing in goal after goal, ably assisted by Chris Sutton or John Hartson.
No midfield of Petrov, Paul Lambert or Neil Lennon providing stability, dynamism and invention. What the former Leicester boss would give for defenders anywhere near the calibre of Johan Mjallby, Joos Valgaeren or Jackie McNamara when he's having to field youngsters loaned from Brentford to patch up his backline.
O'Neill is trying to compete with a resurgent Hearts, an enterprising Motherwell and a rejuvenated Rangers with one of the weakest Celtic squads in years.
Daizen Maeda and Reo Hatate are barely recognisable these days, although the latter is finally showing signs of life. Captain Callum McGregor can only carry a midfield for so many seasons.
Yet the manager is having to coax every last ounce from them. What choice does he have? He's working in an era of Michel-Ange Balikwisha, Joel Mvuka and Junior Adamu.
How then to explain O'Neill's impressive domestic numbers? In his two spells in charge this season he has played 17, won 14, drawn twice and lost only once.
The defeat came when Celtic were down to 10. The draws were at Tynecastle and Ibrox. The spine of the team is now Viljami Sinisalo, Liam Scales, McGregor and Benjamin Nygren, ably assisted by Kieran Tierney and Julian Araujo on the flanks.
They've produced Celtic's first win on German soil, a two-goal comeback away to Rangers and a season-saving victory in Aberdeen.
Despite Hearts' commanding five-point lead, a whisper is emerging from Glasgow's east end: with injured and suspended players due shortly to return – and with midweek matches now largely a thing of the past – is O'Neill nine matches away from his best ever achievement as Celtic manager?
