Ronny Deila's critics are out in force. Groups of angry Celtic fans are gunning for him and their numbers are swelling with every passing week.

It is now 15 weeks since Deila was appointed as Neil Lennon's successor and they have not been a fruitful period. In fact, this 2014-15 football season has so far been damaging to the reputation of the Norwegian.

Shambling along in the league, and bounced out of the Champions League qualifiers in embarrassing and abysmal fashion, Celtic's football so far has offered few glimpses of Deila's ability as a coach.

Indeed, quite a few Celtic supporters have already made up their minds that Deila is their very own Paul Le Guen - a foreign manager who, for whatever reason, simply will not cut it in Glasgow.

Deila's Celtic have so far played 13 competitive matches, of which they have won five, drawn four, and lost four. This is not the stuff of progress.

More worryingly for Deila, following Sunday's dispiriting 1-1 draw at home to Motherwell, is a run of just one win in seven games since Celtic put six past Dundee United in mid-August.

One Celtic supporter said to me this week (expletives deleted): "Get Deila out of here. He is not good enough for Celtic. His appointment was a total disgrace."

When things are as hot as this, you do wonder, looking back to Celtic's chaotic summer, what the club were all about in appointing Deila in the first place.

My own view on Deila's appointment hasn't changed since the day he arrived. I wrote at the time that it was an obvious risk by Celtic, but that it was also bold of the club - and even imaginative - to go for him.

Celtic have done well in recent years in finding talented, unknown players and making good use of them for a few years. Why not try likewise with a manager?

Deila had done significantly well with Stromsgodset in Norway - and over a sustained period of years. There was an unsurprising logic behind his appointment.

Of course, risk is one thing, and even commending that risk is permitted. But it has to work. And Deila right now is struggling at Celtic, which is why Wednesday night's League Cup third-round tie against Hearts in Glasgow is huge for him.

If Celtic lose to a team from a tier below them, Deila will come under immense pressure. There will be calls for his head from among the Celtic faithful which will make Peter Lawwell, the club's CEO, distinctly uncomfortable.

It will all cause recall for the chaotic manner in which Deila arrived in the first place, with Dermot Desmond pulling Celtic in Roy Keane's direction, and Lawwell clearly pulling differently. That aspect of Celtic looked pretty unimpressive.

For me, the worst part of Deila's stuttering reign so far was the incredible botch at home to Maribor in the Champions League play-off on August 26.

For Celtic and their coach to contrive to lose that match, with a monied group-stage place in the offing, was absurd. There is no context here to be made for being "disrespectful to foreign teams". Celtic should have comfortably seen off Maribor over two legs. Instead, they made a fist of it.

Ironically, I still believe a time in the ugly duckling called the Europa League may be beneficial to Deila, just as it was for Neil Lennon in 2011-12 when he got a telling taste of the European scene.

But Deila has to pave his own path to get there. He will not survive at this rate of progress. As things stand, "the risk" in his appointment is looking ominous.

When he arrived in Glasgow in June, Deila said: "My philosophy is to play attractive football, and offensive football. I also want to win trophies." In recent days he has also spoken of his desire to win the treble with Celtic this season.

For the sake of all of that, Celtic cannot countenance defeat to a Hearts team which is growing in self-belief. Such a setback would have some putting the foundations in place for Deila's gallows.