Last season was also marked by a damaging split between the board and sections of the support unhappy at the level of investment in the squad and the general running of the club.
The two sides united for last season’s victorious climax to the season, but the splits have re-emerged.
“Ultimately it always comes down to recruitment, doesn’t it?” Callaghan said. “I hear folks talking about entitled Celtic fans, but millions of pounds in the bank is no use unless you’re spending it.
“It’s about spending more effectively and it’s spending certainly more efficiently and sooner within the window.
“The start of the window was exciting. Camilo Duran is a brilliant player. As good a signing as we’ve made in some time, Mika Baur the same.
“But the defensive midfield has been a serious issue. We haven’t signed anyone there and you’re now starting to feel sorry for Callum McGregor – he’s been hung out to dry.”
Daily Record football writer Michael Gannon agreed that O’Neill had been used as a human shield by the board.
“I feel for him a little bit because he’s the only person at Celtic who fronts up and faces questions on a regular basis,” he said.
“A lot of the questions, like where is the full-time chairman, where’s the head of recruitment, where’s the director of football, what’s happened with the Green Brigade bans and fan problems, are not really for him to answer.”