Speaking further on talkSPORT, the Maggie May hitmaker said the culprits had “brought terrible shame” to his beloved club.
A spokesperson for Celtic said players had been left “shaken” by the event and condemned the violent scenes as “unacceptable”.
They added: “The club will be investigating these events fully.
“For players and a management team, who have given so much in recent years and have delivered 11 consecutive trophies, to require an escort from Celtic Park while being targeted with missiles, is simply unacceptable.
