This wasn't the way Olivier Ntcham was supposed to leave Celtic.

Signed from Manchester City four summers ago for a considerable £4.5m fee, the Frenchman quickly made an impression in Glasgow and looked to be an ideal fit for Celtic's buy-to-sell approach in the transfer market.

Winning three trebles, scoring a last-minute winner against Lazio and settling a derby match against Rangers would ordinarily be achievements associated with an overwhelmingly successful stint at the club and, looking into the future from season 2017-18, Celtic fans might have expected to carry him out of Lennoxtown on a throne as a ten-in-a-row winner and send him on his way to one of Europe's elite clubs in exchange for more than £20m.

Instead, Ntcham is ambivalently sauntering out of Glasgow with a cancelled contract, a stick and bindle over his shoulder the noise of a slamming door ringing in his ears.

The promise he's fleetingly shown in green and white hasn't been consistently reached. Shortly after signing, he scored the goal that put Celtic's Champions League qualifier beyond Astana just as the Kazakhs were threatening to somehow overturn a 5-0 first-leg deficit by leading the second 4-1 with 20 minutes to play.

When he brought Ntcham to the club during that summer of 2017, after watching him for eight months, Brendan Rodgers said: "He has everything. Mentally, it's just a case of him taking the next steps in his career, coming to play at a huge club with big demands and the opportunity to play in the Champions League."

READ MORE: Ange Postecoglou should take a leaf out of Gus Hiddink's book

Fast forward four years, and looking at those next steps, it hasn't really gone to plan. In a two-year loan spell at Genoa, a then-teenage Ntcham achieved 37 Seria A appearances while on loan from Man City - not a bad league in which to take your first steps in senior football. In the last three seasons in Scotland, Ntcham's played exactly 50 per cent of Celtic's league games, probably thanks, in no small part, to having his head turned two summers ago by a sizeable £13m bid from Porto.

Celtic said "thanks, but no thanks" and Ntcham publicly announced his dismay to L'Equipe, citing the level of the Scottish Premiership as the source of his ire: "I was really disappointed not to have gone to Porto," he said. "Celtic have given me a lot, but it's the best solution for my development."

With Celtic losing in the Champions League qualifying stage for the second consecutive season around the time Porto's bid was knocked back, it's hard to put yourself in Ntcham's shoes and think on a differing wavelength. This was a young man who had performed well for the club but grew-up without green and white heartstrings. Striking when the iron is hot is vitally important for footballers and their career trajectories and Celtic poured cold water all over Ntcham's, which they're well within their rights to do if they feel they can tempt a club into a higher offer. Isn't hindsight a wonderful thing?

On the flip side of that, despite being understandably miffed, professional footballers are paid to do a job to the best of their ability and outwith his goal in Rome, Ntcham plateaued, to such an extent in fact that the club linked most strongly with him over the last month has been AEK Athens, ironically one of the clubs that prevented him showcasing his talent in Europe's top competition.

An admission of frustration or unhappiness can often be enough to sever any ties of respect with some Celtic supporters and at that particular time, any player who didn't want to help the club achieve "the ten" was often told they weren't welcome.

Even Kieran Tierney, who had an extremely emotional bond with the club, got it from some angles. Ntcham, despite his iconic goal against Lazio just a few months after announcing he wanted to be wearing a different strip, never really recovered.

Those opportunities highlighted by Brendan Rodgers to play in the Champions League haven't come to fruition. His first season allowed him to test himself against his boyhood club PSG, an emotional attachment that wouldn't help his cause during an infamous loan spell to Marseille during the second half of last season, as well as Bayern Munich.

Despite running the Germans close at Celtic Park, Ntcham didn't feature. The other games were essentially training sessions for the heavyweights and Oli's moment to remember came in Brussels against Celtic's direct competition for third place in the group, Anderlecht, when his perfectly-weighted through-ball for Tierney led to Leigh Griffiths' opener in a 3-0 victory. 

READ MORE: Breaking down Celtic's defending at John Souttar's Hearts winner

Callum McGregor and Scott Brown's places alongside each other in the Celtic team over the last five years have been as sure as the sunset and with Tom Rogic, Stuart Armstrong, David Turnbull and Ryan Christie among a few others to compete with for the other midfield spot, it's quite right there's been no guarantee on Ntcham's starting place and truth be told, when he was given one, he quite often looked bored.

Perhaps a change in manager and the departure of his pal Moussa Dembele deflated his level of motivation along with achieving everything he realistically could have after two seasons with the club.

Postecoglou said earlier this summer he'd had conversations with Ntcham about his future and that the Frenchman "wants to come back and make an impression this year."

Even Chris Sutton, with his pom-poms, backed Ntcham to be a "massive asset" and revive his career in Glasgow's East End this season.

I'm not sure anybody, or certainly the majority, really believed this and instincts on that front have proved correct.

Victor Wanyama, Virgil Van Dijk, Stuart Armstrong, Moussa Dembele and now Kris Ajer are all living proof of Celtic's ability to buy young players, mould them into stars, and sell them for a profit.

For all his quality, Olivier Ntcham is a blot on that copybook. He leaves Celtic Park with his attitude in doubt and his tail between his legs while the decision-makers head back to their office with theirs also tripping them up.

Nobody has really won in this rather sorry saga.