Kristoffer Ajer singled out Celtic assistant manager John Kennedy for praise as he said farewell to Hoops fans following his move to Brentford.
The Norway international said the quadruple treble, won by the Hoops under Brendan Rodgers and Neil Lennon, would never have happened without Kennedy, who worked under both managers.
Ajer scored the winning penalty against Hearts to seal the historic feat in the 2020 Scottish Cup Final and played a key part as Celtic lifted 12 trophies in a row in four years.
The 23-year-old, who completed his move to the English Premier League newcomers on Wednesday, also hailed the size of the Parkhead club and thanked the fans for their support.
He wrote on his Instagram account: “5 years ago I travelled to Glasgow not knowing what to expect. The stories I got told seemed incredible, but the very first time I walked out at Celtic Park I truly understood how big a club Celtic really is.
“’Football without fans is nothing’, and I want to thank every supporter that has contributed to making my time at Celtic so special.
“I also want to thank the managers that have developed me as a player, back room staff that has helped me through ups and downs, and also my teammates that have become great friends that will last a lifetime.
“A special mention also to John Kennedy, the most important person for me during my time at Celtic. Without him, we would never win the quadruple treble.
“I wish everyone that loves Celtic a successful future, I will always support the club.”
Celtic announced a deal to bring in a replacement centre-back in the shape of Sweden international Carl Starfelt from Rubin Kazan shortly after Ajer’s departure was announced.
The 26-year-old is joining on a four-year deal once his quarantine period is complete.
Celtic manager Ange Postecoglou told the club’s website: “Carl is an experienced player and someone with the attributes to be a real success at Celtic.
“He is a strong, athletic and committed defender and will add quality to our squad. I am sure he will be a player our supporters will welcome warmly and someone who will be really important for us going forward.”