Neil Lennon's second reign as Celtic manager is over, with the defending champions trailing by 18 points in the Scottish Premiership race.

There have been four league defeats, two of them to Rangers, who are way out in front and still unbeaten.

A fourth successive clean sweep of trophies was completed in December but the team that started 2020 with 12 domestic wins and one draw to reach the Scottish Cup semi-finals and wrap up nine titles in a row in a truncated season has spiralled out of form to lose their stranglehold on success.

BBC Sport Scotland looks back at the pivotal matches in that fall from grace.

Celtic 1-2 Ferencvaros, Champions League qualifier, 26 Aug

The Champions League was never going to be Celtic's priority this season with the prize of a record 10th consecutive league title on offer. But the least fans expect is a respectable showing.

This season's format was different. One bad result and you were out, as Lennon learned the hard way.

The Scottish champions opened with a big win over KR Reykjavik but then suffered their earliest exit in 15 years after a shock defeat at home to Ferencvaros.

New goalkeeper Vasilios Barkas did not look to clever for Tokmac Nguen's decisive breakaway goal, while the decision to use Ryan Christie as a makeshift striker in the absence of Odsonne Edouard raised a few eyebrows since Albian Ajeti and Patryk Klimala were on the bench.

Celtic 0-2 Rangers, Scottish Premiership, 17 Oct

Celtic went into the first Old Firm derby of the season on the back of eight straight victories.

Both sides were unbeaten domestically but Rangers ran out comfortable winners at an empty Celtic Park as Connor Goldson exposed the defensive frailties that would become a recurring theme with both goals.

The hosts, without Edouard and Christie due to Covid-19 cases on international duty and the injured James Forrest, failed to register a single shot on target in a passive performance, amid line-up leaks from inside the club.

Having been outplayed, Lennon said afterwards: "We have to roll our sleeves up and do better."

It marked the start of a dismal run of just two wins in 12 outings.

Celtic 1-4 Sparta Prague, Europa League, 5 Nov

Despite being number one seeds, Celtic landed in a tough Europa League group and opened with a sobering home loss to a resurgent AC Milan on the back of that defeat by Rangers.

A draw away to Lille followed, leaving Lennon's men looking for positive results against Sparta Prague to revive hopes of reaching the knockout round.

Instead, a horror show ensued at Celtic Park, with the out-of-form Czechs, who were missing several key players, romping to a 4-1 win and looking like they would score from every counter-attack.

The same scoreline was repeated in Prague three weeks later, snuffing out any chance of qualification with two games remaining.

Celtic 0-2 Ross County, League Cup, 29 Nov

That result in Prague piled the pressure on Lennon. It was clear he could not afford any more slip-ups but now a more favourable set of fixtures seemed to be upon the horizon.

Ignoring the remaining Europa League ties, which were no longer of any great relevance, Celtic could look forward to league matches with St Johnstone, Kilmarnock and Ross County at Celtic Park and a delayed Scottish Cup final against Championship side Hearts.

First up, though, was a League Cup tie at home to Ross County, who had taken two points from their previous seven league games and had never won at Celtic Park before.

Stuart Kettlewell's men inflicted a 2-0 defeat against lethargic opponents, with Celtic players and management needing a police escort from the ground because a group of supporters turned up to vent their frustrations.

Days later, the board issue the first of a series of statements backing the manager, although a later endorsement promised a review in the new year.
Celtic v Ross County

Rangers 1-0 Celtic, Scottish Premiership, 2 Jan

This was a game Celtic really had to win to have any chance of reeling in Rangers.

More points were dropped with a draw at home to St Johnstone but there followed a heartening run of six wins, including the delayed 2019-20 Scottish Cup final against Hearts, which clinched a quadruple treble, with midfielders David Turnbull and Ismaila Soro breaking into the starting XI and showing signs of promise.

Tails were up and Lennon's side started strongly at Ibrox, pinning the league leaders back for most of the first half, while Allan McGregor denied Leigh Griffiths with an outstanding save.

However, the contest was more even after the interval and the visitors were reduced to 10 men following Nir Bitton's rash decision to haul down Alfredo Morelos. Soon after, a corner was deflected into his own net by Callum McGregor.

The harsh loss was their third successive derby defeat and left Celtic 19 points behind their great rivals, with the beaten side flying out to Dubai for a much-criticised training camp just hours later.

Livingston 2-2, Scottish Premiership 20 Jan

Celtic had hoped to return from the Middle East rejuvenated for the second half of the season and one last push for 10-in-a-row. Instead, they were left in tatters.

Injured defender Christopher Jullien tested positive for Covid-19 on return and that led to 13 other players being instructed to isolate, along with Lennon and assistant John Kennedy.

A depleted side was held to draws at home to Hibernian and Livingston and 2021's winless run continued with another share of the points in West Lothian.

Ciaron Brown headed Livingston in front, with Celtic replying with goals from Mohamed Elyounoussi and Nir Bitton. Jay Emmanuel-Thomas levelled after the break and the evening got worse for the visitors when captain Scott Brown was sent off five minutes after coming off the bench.

A run of four league games without a win is the club's worst since 2000 but Lennon insisted: "I won't walk away, absolutely not."
Celtic 1-2 St Mirren, Scottish Premiership, 30 Jan

With their squad restored to near-full strength, Celtic could simply not afford to drop any more points, and hope for a spectacular collapse from title-chasing Rangers.

Instead, another humiliating loss transpired, with St Mirren claiming their first win over Celtic in eight years, and their first victory at Celtic Park in more than three decades.

Ilkay Durmus and Kristian Dennis struck either side of Odsonne Edouard's reply amid slapstick home defending.

Lennon described the defeat as the lowest point of his Celtic managerial career and asked if the players were letting him down, replied: "Honestly, at this minute I think yes, they are. And they have done for quite a while this season."
Ross County 1-0 Celtic, Scottish Premiership, 21 Feb

The defeat that clinched Lennon's fate.

County were bottom of the table heading into Sunday's game in Dingwall, and rank outsiders to beat Celtic for the second time this season.

The visitors had won five games in succession, scoring 13 goals and conceding just two, but failed to capitalise on a glut of chances in either half, Edouard and Christie spurning the best of them.

Yet again, a set-piece was to prove their downfall. County's towering striker Jordan White was left unmarked from a free-kick, and nodded the only goal of the game past Scott Bain.

Lennon said after the game that he would "carry on his duties as normal", and later walked out of his post-match interview following several further questions on his future at the club.