Former Celtic striker John Hartson believes mistakes made in player recruitment played a part in Neil Lennon's downfall this season.
Hartson, who scored 88 goals in 146 games during five years at Parkhead, feels Lennon's failure to guide the club to a 'Holy Grail' of 10 titles in a row was down to several factors, with poor performance in the transfer market a critical one.
The former Welsh international highlights the large fee paid to AEK Athens for goalkeeper Vasilios Barkas and a failure to pursue Peterborough striker Ivan Toney, who went on to join Brentford and is the leading goalscorer in the Championship, as costly errors.
"It's all gone desperately wrong," Hartson told Sky Sports News. "It's a pivotal moment and Neil shouldn't be held accountable for all of the things that have gone wrong.
"You have to look at the recruitment - was paying £5m for Barkas, a goalkeeper who isn't even in the team and hasn't made a decent save all season, a good piece of business for Celtic?
"They could have got Ivan Toney for another £500,000, I don't know why they didn't go and get him.
"They need to get it right because Celtic have been so successful in the past 10 years and this was a massive year for them and the supporters. This was the Holy Grail for them, if they could get 10 (titles). And it's not been acceptable the way the team has dropped so low.
"I was telling people Celtic would win 12, 13, 14 titles in a row, that's how dominant they were. Rangers have had a good season, they've capitalised on Celtic's poor performances and are doing very well in Europe. They will certainly win the league now too."
Hartson feels getting the appointment of Lennon's successor at Celtic is now vital because of the size of the club.
"They need to get the next appointment right," he said. "I've heard Eddie Howe mentioned, Steve Clarke the national manager is an obvious one and he's a Celtic fan, sometimes they go for someone who has an affinity with the football club.
"Mark Hughes is out of a job. It's a massive job, it's a global football club with incredible support and Neil should be respected because he's done very well in terms of his playing and managerial career there but it was the right time."