The Swede, who will leave his role as assistant manager to Neil Lennon when his contract expires on May 12, watched Virgil van Dijk in Groningen's final Eredivisie match of last season - a 2-0 home defeat to Ajax in which he looked none too clever at either goal - and reported back to the board that signing him was a "no-brainer".
He also takes great pride in the fact he put the squeeze on van Dijk over the summer, in the same way he used to impose his own particular force of will on centre-forwards, to make him realise there has to be a considerable amount of dirty work done in defence along with the technical elements in which he has shown himself to be more than proficient during an impressive debut season in Scotland.
Of course, this debut season in Scotland may prove to be the 22-year-old's last. The public pronouncements of his agent, Henk-Maarten Chin, suggest there will be offers forthcoming from south of the border this summer and, given the current financial climate, they may prove difficult to turn down.
Mjallby accepts part of his role at Parkhead lies in polishing rough diamonds and preparing them to be auctioned off at inflated rates and is clear where the bidding ought to start should this particular gem find himself the subject of concrete proposals over the next few months.
"I definitely think he is worth at least £8million," he stated. "If he keeps improving, he is going to be a superstar." Whether van Dijk remains in Glasgow or opts to try his luck elsewhere, Mjallby has no doubt that his career trajectory will, in time, take him to a top four team in England or a club of similar stature on the continent.
"I would be surprised if he doesn't play for a top, top team in the future," he said. "Virgil is so good on the ball with deceptive pace.
"When he first came here, he wanted to play football and didn't want to do the dirty bits, so we were quite hard on him in pre-season.Technically, though, he is one of the best centre-halves I have ever seen.He is very good in the air defensively, too, but could improve in terms of scoring goals from corners."
Mjallby, as a player, was cut from a different cloth than van Dijk. He was the type of footballer, right knee in pieces or not, who made you believe that talk of running through brick walls might be more than just an analogy. He admits, though, that, in putting together Celtic's successful central defensive partnership of van Dijk and Efe Ambrose, he made it clear that players of his ilk are no longer what is required to prosper in the modern game.
"Since day one, we insisted that we weren't looking for Johan Mjallbys any more," said the 43-year-old, who felt Celtic were losing far too many goals when he joined up with Lennon four years ago and is delighted with the progress made in rectifying that problem.
"Neil and I wanted to have two pacy centre-halves. We have most of the possession in domestic games and most chances the opposition create are going to come from counter-attacks. In Europe, most teams have pace as well and that has been a good partnership for us.
"I am sad about leaving this group of players. It has been brilliant improving most of them and that is where Celtic is aiming now - getting younger players in and, hopefully, selling them on."
Emilio Izaguirre was another player plucked from obscurity by the Celtic scouting staff, brought from FC Motagua for a pittance four years ago and now preparing to travel with Honduras to the World Cup. He played his last game of the season for Celtic against Aberdeen yesterday and, as he prepares to head off on a short break before reporting for duty with his country in Miami at the end of next week, admits he is now depending on the club captain Scott Brown to make sure he receives a winner's medal from the SPFL.
"I am upset that I cannot be around for the trophy presentation at the weekend, but the manager and I think it is good for me to have a holiday," said Izaguirre. "I have been reminding Broony every day to send me my medal."
Honduras play England in a warm-up match in Miami on June 7 and Izaguirre hopes to play against team-mate Fraser Forster, a man he believes must be given a chance to represent the Three Lions in Brazil.
"I feel lucky to be working with one of the best keepers in the world," he said. "He deserves to be in the England squad and that would be an opportunity for him to get a game."