THE biggest lesson that Ronny Deila should have learned from the defeats to Legia was that he can't afford to go with his preferred option of playing only two holding midfielders in vital European ties.
In domestic games it might work fine to have just two sitting deep while the three midfielders ahead of them try to support the lone striker.
But against European teams, even more so away from home, it leaves the Hoops wide open to counter-attacks. Especially when the full-backs are being encourage to push on.
The Hoops defence needs the protection offered by three midfielders playing directly in front of them so the width of the pitch can be covered better.
The two wide midfielders can track back and also support the striker when required. This 'Christmas tree' formation is much more secure and should provide a safer platform from which Celts can get the positive result they want in Slovenia.
CAUTIOUSLY says HUGH MacDONALD:
The answer in numbers is 4-2-3-1 or 5-4-1 but Deila is more likely to go for the former.
He can bring back Mikael Lustig to add to his defensive strength and should play both Stefan Johansen and Charlie Mulgrew as holding midfielders in front of his centre backs.
The Legia lesson must be learned. In Poland, Celtic went in front but were recklessly adventurous, even after the dismissal of Efe Ambrose.
This Champions League reprieve must be capitalised on by ensuring Maribor travel to Celtic Park with the tie still open. This calls for defensive solidity in Slovenia.
Resilience could be the basis for a counter-attacking strategy that would suit such as Derk Boerritger and even Leigh Griffiths, though he can only expect a place on the bench.
Deila is an idealist in terms of attacking. He must be a realist if Celtic are to sustain any hopes of progressing to the Group Stages of the Champions League.