"Then in the second goal, we had a 2v2 situation, and we allowed the player just to come inside and bend it into the net.

"So from our viewpoint, not good defending, really."

The need for O'Neill to explain the concessions in such layman terms speaks volumes. Damning volumes.

While Midtjylland were majestic, Celtic didn't exactly make them work hard for their money.

"The third goal almost puts it beyond you, so was I surprised? I don't know whether I was surprised [or] disappointed, just disappointed in the concession of the goals," the Northern Irishman added.

"I think just to play football at the top level, not only do you need ability, but you need mentality, and mentality sometimes overrides ability as well.

"It sounds from here as if I'm like a teacher telling them, but I will try and teach them the game as quickly as possible.

"Things that they may already know, may need reminding, maybe they don't know, and it's my job to try and improve the football club."