Falling 18 points behind leaders and Old Firm rivals Rangers with eight games to go has prompted the club hierarchy to act – after a season of slip-ups, sub-par performances and protests.
Speculation and rumour has been rife on the manager’s future for some time – and the betting markets on his successor have been ever-changing.
We look at who could be stepping in for the former Hibs and Bolton boss as his second spell in charge at Parkhead comes to an end.
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9. Xabi Alonso
Currently coach of Real Sociedad's reserve side, the former Liverpool midfielder would meet former team-mate Steven Gerrard in Glasgow and was touted for a role by ex-Hoops striker Charlie Nicholas (CHRISTOF STACHE/AFP via Getty Images) Photo: CHRISTOF STACHE
10. Xavi Hernandez
Another coach tipped by Nicholas as a potential candidate last month, the former World Cup winner is currently plying his trade in the lucrative Qatari League (Photo by KARIM JAAFAR/AFP via Getty Images) Photo: KARIM JAAFAR
11. Ralf Rangnick
Football revolutionary who could have a big impact on the structure and football cultture at Celtic with his ideas. Another whose name has popped up frequently, German would be an interesting, if bold, candidate with a strong background and football philosophy. Photo: ODD ANDERSEN
12. Andre Villas Boas
Big name credentials and has a CV including some big clubs in less glamourous leagues and is currently in strained relations with Marseille over the transfer of Olivier Ntcham from Celtic. Photo: CHRISTOPHE SIMON