NEIL Lennon reiterated in the aftermath of Celtic’s dire defeat to CFR Cluj at Parkhead last night that he remained determined to strengthen his squad with new players before the transfer window closes at the end of this month.

Using some the £25 million that was received from Arsenal for Kieran Tierney last week to bring in a new left back, another right back and possibly an additional striker in the coming fortnight will go some way towards placating seething supporters after their ignominious Champions League exit.

But perhaps the most important signing the Scottish champions could make in the days ahead is a Director of Football or, at the very least, a permanent Head of Recruitment.

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Many reasons have been put forward for Celtic’s painful and costly failure to reach the group stages of Europe’s premier club competition for the second consecutive season and the fourth time in six years.

Lennon’s decision to play midfielder Callum McGregor out of position at left back was one. Being too gung ho defensively and leaving themselves exposed at the back was another. The manager himself felt his charges’ lack of ruthlessness up front cost them and with good reason. They passed up a glut of opportunities in the final third and paid the price.

Yet, major shareholder Dermot Desmond, chief executive Peter Lawwell and their fellow directors must shoulder their share of responsibility for what was, given the strong financial position they are in, an unforgivable loss against mediocre rivals.

Poor recruitment, specifically their inability to bring in an adequate replacement for Tierney early enough in pre-season for him to bed into the side, is ultimately what is to blame for this embarrassing setback.

READ MORE: Neil Lennon admits Champions League exit could affect his ability to strengthen the Celtic squad

Yes, Lennon was, as his predecessor Brendan Rodgers had been when he did the same thing in a Ladbrokes Premiership game against Rangers at Ibrox back in December, wrong to move McGregor to left back.

The Scotland internationalist looked uncomfortable and the entire Celtic team failed to function as effectively without their talisman dominating possession as usual in the centre of the park.

But what alternative did Lennon have? Boli Bolingoli had been woeful in the first leg in Romania six days earlier and had gifted ordinary opponents a goal against the run of play. He had no other options, no other specialist left backs, in his squad.

That is an incredible position for a club like Celtic to be in going into a fixture of such massive importance.

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Bolingoli, a £3.5 million acquisition from Rapid Vienna last month, may recover from a difficult start to his time in Scotland and justify the outlay it took to secure his services. He has certainly fared far better against St Johnstone and Motherwell. But there is already a strong suspicion that the Belgian is not up to the task.

The business Celtic have conducted in the last five transfer windows under former head of recruitment Lee Congerton and his part-time replacement Nicky Hammond hardly fills supporters with confidence.

Olivier Ntcham, Odsonne Edouard, Scott Bain and, to an extent, Jonny Hayes have all proved good buys during that period. Filip Benkovic excelled during his loan spell. But the less said about Kundai Benyu, Marvin Compper, Jack Hendry, Emilio Izaguirre, Youssouf Mulumbu, Charly Musonda and Jeremy Toljan the better. How will Bolingoli, Hatem Elhamed and Christopher Jullien do going forward? The jury is out.

But the fact that Hammond, the former director of football at Reading and technical director at West Brom, was only brought in to replace Congerton, who joined Rodgers at Leicester City in May, in June to work “across the summer period” was clearly far from ideal. It suggested it was a knee-jerk appointment, a stop gap measure.

Both left back Bolingoli and centre half Jullien, a £7 million capture from Toulouse in June, sat out the Cluj match and the makeshift defence that started the third round qualifier looked disjointed and shipped four goals at home. It was a highly unsatisfactory and entirely avoidable state of affairs.

Celtic have had many triumphs in the transfer market as well as on the field of play in the past decade and have made tidy profits as a result of both. But the consistent domestic and European successes and multi-million pound sales of Victor Wanyama, Virgil van Dijk and Moussa Dembele have been down to having a professional and proven recruitment team headed up by John Park.

They must invest in the structure of the club, not just splash money haphazardly on new players who aren't of the requisite quality, and appoint Hammond or another candidate on a full-time basis to a Director of Football role if they are to continue to dominate in Scotland and fare well in Europe.

Their last annual results showed they had £27 million in the bank and their revenue had exceeded £100 million. Since then they have offloaded Dembele to Lyon for £20 million as well as Tierney to Arsenal to £25 million. So they aren’t exactly short of the money needed.

Celtic have excelled at identifying young players who can be bought for an affordable price and whose raw talent can then be developed. Will Kristoffer Ajer, Ntcham or Marian Shved go for big bucks in the seasons to come? Don’t bet against it.

READ MORE: Celtic 3 CFR Cluj 4 (aggregate 4-5): Neil Lennon's side crash out of Champions League

But having a first team that is good enough to make it through to the Champions League group stages, something which will bank them in excess of £30 million, has to be their priority.

Relations between Lawwell and Rodgers deteriorated towards the end of the latter’s tenure due to disagreements over recruitment. Lennon is likely to be more accepting of the restrictions there are on spending than his compatriot who was used to operating in the Premier League in England. But he must be firm, too, to avoid further humiliations in future. Keeping his job will depend on it.