THE 2-1 defeat that Celtic suffered to Kilmarnock at Rugby Park on Sunday meant the Parkhead club has now made their worst start to the league in 20 years.

Brendan Rodgers, their manager, has admitted that supporters should be alarmed at how his men have been performing.

So how have his men gone from double treble winners to sixth in the Ladbrokes Premiership in the space of little over three months? Here we examine four things which have contributed to their slump.

A DISASTROUS TRANSFER WINDOW

Celtic’s summer recruitment drive started so encouragingly with the signing of Odsonne Edouard from Paris Saint-Germain for a club record £9 million fee back in June.

The 20-year-old striker showed, not least in league wins over Rangers at Ibrox in March and then Parkhead in April, what an exciting prospect he is during a season-long loan spell in Glasgow last season.

But after Edouard had arrived things quickly went downhill.

The failure to land John McGinn – the Scotland internationalist who was, it seemed to many knowledgeable observers, the natural successor to skipper Scott Brown in central midfield – from Hibernian was needless and perplexing.

McGinn, a lifelong Celtic supporter, was available for an affordable fee. But playing hard ball with Hibs over the asking price backfired spectacularly. After an impasse that dragged on for weeks he opted to join Aston Villa.

Supporters are entitled to ask why that approach was taken. After all, the Scottish champions last week announced that they enjoyed record sales revenues of over £100 million in the last financial year and have £27 million in the bank.

The 23-year-old Scotland internationalist has been nothing short of a revelation at Villa Park and scored what will unquestionably be a strong contender for English Championship Goal of the Season come May against Sheffield Wednesday on Saturday.

What would Brendan Rodgers give to have a player with his drive, physicality and ability in his side just now? A lot more than what was offered to the Easter Road club in the close season.

Bringing back Emilio Izaguirre, signing Youssouf Mulumbu on a free transfer and agreeing loan deals with Daniel Arzani and Filip Benkovic has done little if anything to placate supporters. Or, for that matter, their manager. The tensions between him and the board have not been difficult to detect.

DEPARTURE OF KEY PLAYERS

Complacency is fatal in football. Celtic may have won six domestic tournaments in a row. But they still needed to strengthen. The departures, for hefty fees, of Stuart Armstrong and Moussa Dembele, has made them weaker.

SCOTT SINCLAIR’S LOSS OF FORM

Has any player in Scottish football history ever gone backwards quite as spectacularly as Scott Sinclair? It is hard to think of one.

The former Swansea City and Manchester City winger was superb in his debut season in this country. He was Brendan Rodgers’s star man as Celtic went undefeated to win only their fourth domestic treble. He rightly scooped every Player of the Year award going.

Since then? Sinclair has been disappointing. Yes, he netted 18 goals in all competitions in the 2017/18 campaign to finish top scorer as the Parkhead club retained all three domestic trophies and reached the last 32 of the Europa League.

But he was a shadow of his former self. That has continued this term. So much so, that he is no longer considered an automatic first choice.

But this is a man who cost £3 million and is by far and away the highest earner at Parkhead. The 29-year-old isn’t providing value for money at the moment and hasn’t done so for some time.

TOO MANY GAMES HAVE TAKEN THEIR TOLL

Brendan Rodgers freshened his side up against Kilmarnock on Sunday. Jack Hendry got back in, Mikey Johnston received another start, Youssouf Mulumbu made his debut and Ryan Christie got the nod. But Celtic still laboured.

Is the number of games that their key protagonists have played for club and country in the past couple of seasons the reason for the flatness of their displays?

Mikael Lustig, the 31-year-old right back who played for Sweden in the Russia 2018 finals this summer, certainly looks in desperate need of a lengthy rest. The same goes for a fair few of his team mates.

This season Celtic have were required to play in another round of European qualifiers. They needed to take part in no fewer than eight fixtures to reach the Europa League group stages. It isn’t getting any easier for them. And they have, as has been previously mentioned, fewer top players to call on.

The high-pressing game that Rodgers ask his team to play is demanding. It is unreasonable to expect key personnel to execute it week in, week out, both domestically and in Europe without . Dips in form are inevitable if they are continually being asked to produce.

But is there enough quality in the Celtic squad to allow the likes of Scott Brown, James Forrest, Callum McGregor, Kieran Tierney and Sinclair, who all played more than 50 games last term, to take an extended break? It appears, on the evidence of the weekend at least, that strength in depth is lacking.

EDOUARD HAS FAILED TO JUSTIFY HIS FEE

It is worth pointing out that, despite the £9 million that Celtic lavished on him this summer, Odsonne Edouard only turned 20 in January. The France Under-21 internationalist has still played fewer than 50 games of senior football. His huge fee reflects his future potential as much as his current ability. He is a young man plying his trade in a foreign country and allowances must be made for that.

Edouard has shown glimpses of what he is capable of this term. His double against Rosenborg in a Champions League qualifier this term helped his team reach the third qualifying round. But the former Paris Saint-Germain youth player has hardly been prolific. He has now gone six games without netting.

With Moussa Dembele having departed and Leigh Griffiths returning from injury Celtic haven’t been anywhere near as formidable in attack.