At 12.35 this afternoon, four days on from his 90th birthday, Sean Fallon will take centre stage at Celtic Park.

It is not a position he is accustomed to. Although few have contributed more to Celtic's 125-year history than the man unfurling the league flag, Fallon's three decades of sterling service were spent almost entirely in the shadow of others. From the fearless, unfussy full-back who watched Charlie Tully soak up the adulation, to the loyal assistant at Jock Stein's side, he was rarely the man in focus.

With Stein not around to laud his input, and Fallon himself humble to a fault, the result is a hero who – if not exactly unsung – has gone largely underappreciated. That conclusion was reinforced recently when some supporters, albeit a minority, grumbled about the 90-year-old being chosen over Fergus McCann for today's ceremony. Even forgetting the 250-plus appearances, the winning goal in the 1954 cup final and his contribution to Celtic's greatest Old Firm win, Fallon's influence during the Stein years ought to have shielded him from such ingratitude.

His signings alone should guarantee unqualified acclaim. When Celtic fans were polled for the club's greatest-ever team in 2002, more than half the final XI shared the distinction of having been recruited by the man from County Sligo. "That was one of Sean's great talents," acknowledged Jim Craig, who missed out on the right-back slot to Danny McGrain, another Fallon signing. "A good number of the Lisbon Lions, myself included, were either brought in by Sean or on Sean's prompting. And the Quality Street Kids were very much his boys."

Nor did the talent-spotting end with Dalglish, McGrain, Macari, Connelly and Hay. Among Fallon's final signings were two teenagers, Paul McStay and Pat Bonner, who would still be playing for the club four-and-a-half decades after he himself had first pulled on the jersey. Given this proven aptitude for unearthing gems, it's no wonder that Stein – a notoriously reluctant delegator – saw the wisdom in backing his assistant's judgment. "Jock trusted me," said Fallon. "If I liked a player, he would be happy for me to get it done. There would be no double-checking to see if I was right. He knew I wouldn't sign anyone I didn't believe was up to the job.

"Scouts would come to me every day with new players to recommend and I'd check them out personally. And the scouts weren't always right. I'd look for ability and potential, but also at whether a boy's mentality was right. Not everyone I signed went on to become a Dalglish or a McGrain, of course. But I do like to think I had an eye for a player and that I got more right than I did wrong."

Fallon's understated assessment is typical of a man who could, with justification, boast of having signed more world-class players than anyone in the history of Scottish football. Yet it is this kind of humility that has allowed credit for many of his most eye-catching acquisitions and achievements to be apportioned elsewhere. Bonner, for example, will recount how he was spotted and signed by his fellow Irishman, but continues to be referred to as Stein's final signing.

Not that the absence of public recognition rankles. As Fallon said: "The players and the people within the club at that time knew I was signing these boys, and that was good enough for me. Anyway, everything I did, I did for Celtic – not for Sean Fallon. I didn't think of the likes of Kenny and Danny as 'my signings'. They were Celtic's signings, and I was just happy to have played a part in bringing them to the club. I never felt the need to crow about it. Looking for good players was part of what I was paid to do."

Another unwritten but equally important aspect of Fallon's duties was complementing Stein's abrasive, if hugely effective, style of management. Whether it was in healing rifts or soothing bruised egos, he was expected to calm irate players while simultaneously reinforcing the message from the man in charge. "Sean played that role brilliantly," remembers Billy McNeill. "And Jock, for all his qualities, needed someone like Sean. He brought to the table all the things that the Big Man wasn't particular good at."

This proves to a recurring conclusion among players from McNeill's era, although Fallon characteristically dismisses the suggestion that he was indispensable to his former vice-captain. "Jock is up there with the greatest managers there has ever been," is his verdict. "He would have been successful in any era. His reading of a game was second to none and he could pick up on the smallest details quicker than anyone. And he was outstanding at getting the best out of players, which is the hallmark of any top manager. He was also a great friend. The four of us – Jock, myself and our wives – would go out every Saturday night together. And even then, Jock and I still talked about nothing but football. We both lived for the game, and for Celtic."

And nobody, one suspects, would be happier than Stein to see a little of Fallon's devotion repaid today.

n BackPage Press will be publishing Sean Fallon's autobiography next year. It is the first time this Celtic legend has told his story, and you can find out more by following @SeanFallonCelt on twitter.