THAT a major overhaul of the Celtic squad was required this summer was widely accepted before their final meeting of the season with Rangers at Ibrox on Sunday.

Just how big that rebuilding job will be, though, was only driven home in the defeat to their city rivals in their penultimate Ladbrokes Premiership match in Govan.

The Parkhead club were flat, devoid of imagination and fortunate only to lose by a two goal margin at the end of 90 one-sided minutes.

The display and result will have been alarming for supporters even though their team had won their eighth consecutive Scottish title the weekend before and are on the brink of making history by completing an unprecedented treble treble.

It shouldn’t be forgotten that Dedryck Boyata, Ryan Christie, James Forrest, Leigh Griffiths and Kieran Tierney, half of their outfield players, were absent.

But the urgent need to freshen up the squad with several quality acquisitions this summer if their resurgent city rivals are to be pipped to the silverware once again next season is obvious.

Boyata, Cristian Gamboa, Emilio Izaguirre and possibly Mikael Lustig will move on, Oliver Burke and Jeremy Toljan look set to return to their parent clubs when their loan spells expire while the futures of Filip Benkovic, Nir Bitton, Marvin Compper, Dorus De Vries, Craig Gordon, Jack Hendry, Eboue Kouassi and Scott Sinclair are uncertain.

The Celtic recruitment department, whose head Lee Congerton joined former manager Brendan Rodgers down at Leicester City at the weekend, have a busy few months ahead of them.

Yet, Peter Houston, the ex-Scotland assistant and Dundee United and Falkirk manager, has complete faith in his former colleagues being able to unearth some diamonds in the transfer market in the close season who ensure their domestic dominance continues.

Houston worked as a scout for the Scottish champions in 2014 – during which time he helped to bring in Norwegian internationalist Stefan Johansen - and was taken aback at the lengths they went to in order to identify and sign players.

“The professionalism of the staff and the way they went about their business, with John Park leading it all, was very good,” he said. “No stone was left unturned. They checked out, they followed up, they watched, they made their move.

“In the scouting department they have all the facilities, all the back-up, they need. It is a fantastic operation. Having been a coach, an assistant manager and a manager throughout my career, it was interesting to get a chance to do the scouting side of it and see how much in-depth analysis went in to trying to find a player. It is quite incredible.”

Celtic have a proven track record of signing little-known youngsters, developing them over time and then selling them on for multi-million pound profits; they have done so successfully on numerous occasions in the past with the likes of Moussa Dembele, Fraser Forster, Gary Hooper, Ki Sung-yueng Virgil van Dijk and Victor Wanyama.

Houston was impressed at how seriously they took the process and how successful their results were.

“Celtic at that time in my opinion were doing it properly,” he said. “You just need to look at John Park’s successes. Yes, there are always failures. But you show me a manager who hasn’t made a signing that hasn’t worked out right and I won’t believe it.

“What Celtic do is they do their analysis, they find out more about them, they send scouts to watch them. I was one of them. I went to watch Stefan Johansen in Tromso. That was built up over a while with a variety of different people watching him.

“(Virgil) Van Dijk was the same I am told. One of the scouts, Neil McGuinness, went out to watch him in the Netherlands, that was followed up by John Park doing the same and he then felt that Neil Lennon, Johan Mjallby and his backroom staff at that time had to see the lad.

“Neil did his due diligence, went and watched him and within a couple of days that deal was done. Just look at what Virgil has gone on to achieve. As well as Van Dijk there was Victor Wanyama and Ki Sung-yueng. A lot of people forget about him, but he was sold for £6 million which is a lot of money in Scottish terms.

“There is a lot of work that gets done. People outside of football, outside of Celtic even, don’t know the work that goes into it. There is a lot of background digging to do. That isn’t just finding out about an individual being a good player, it is finding out about their mentality, their attitude, their commitment.

“These are massive things. You can be the most talented player in the world, but if your attitude stinks then you can sometimes be a liability in many ways.”

Lennon has been helping Celtic in their efforts to bring in new players during the summer transfer window and Houston anticipates he will not be short of options.

“There is a database of players that has been watched by the scouting set-up,” he said. I looked in to it sometimes and it was interesting to see exactly what players had been watched and targeted before my time.

“They used to say: ‘What are you needing Neil? What do you think you are looking for the beginning of next season?’ He would tell us he was after a central midfield player, a centre half.

“The scouting department would then go and rack up four or five affordable names. The video analysis boy would then cut up footage and show them it. Then it was up to them to send in a member of the backroom staff, one of the coaches, to go and watch the player. Then it was taken to boardroom level where they decided if they could afford it.

“I was very impressed indeed with what I saw. It was a great learning curve.”