Martin O'Neill was left to lament a defensive horror show after Celtic crashed to a Europa League defeat against FC Midtjylland.

In his third match at the helm since taking interim charge, O’Neill’s side were dismantled by a Midtjylland team who are flying at the top of the table.

The Danes scored three goals in eight minutes towards the end of the first half on a night which leaves Celtic’s hopes of progression hanging by a thread.

The visitors netted a late consolation via a penalty from Reo Hatate, but it was a major reality check after the recent feelgood factor around the club following O’Neill’s arrival.

Celtic are also set to be without young striker Callum Osmand after he was stretchered off in the closing stages with a hamstring injury.

It was a torrid night for Celtic and Scotland right-back Tony Ralston, who was at fault for both of Midtjylland’s first two goals.

Admitting that the team’s defensive display was nowhere near good enough, O’Neill said: ‘It was a tough night for us, no question of that.

‘We were in the game for half an hour, we conceded two goals within a minute or 90 seconds of each other, and the game goes away from you very, very quickly. They score a third and it’s then a long way back.

‘The goals we conceded weren’t good, but eventually, that hadn’t really much to do with physicality in the sense that we left [players] one-v-one.

‘I’ve just said to the players in there, some things change in the game, other things don’t change.

‘Once a player starts to take you on, let’s say a winger takes you on at full-back. You’ve got to stop him from getting into the penalty area and you have to engage him before he gets there because once he gets in there, then he’s as safe as anything.

‘It’s a safe place for him because the minute that you might put your foot in, you could give away a penalty. Attackers, that’s the one thing they want to do, get one-v-ones.

‘They want to get at the players and they want to get into that penalty area as quickly as possible. So we didn’t do that very well.

‘Then in the second goal, we had a two-v-two situation and we allowed the players just to come inside and then the ball’s into the net. So from our viewpoint, not good defending.’

On the mentality of the team conceding three goals in such quick succession, O’Neill continued: ‘You’ve got to hang in, that’s really it. You have to regroup, whatever you do, you don’t concede a second goal. It came as a bit of a shock.

‘It’s something that you have to do. 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.

‘I’ve seen players with lesser talent but more drive and more determination come through and players who have the talent but don’t have that mentality fall by the wayside.

‘But in terms of European football, Midtjylland are a very fine side, there’s no question about it. They’re strong, physically very, very strong.

‘It was something that I knew anyway because I’d seen them a couple of weeks ago [against Nottingham Forest]. It was a bit disappointing, but I thought that we showed the character in the second half.

‘We could have gone under, it could have been any sort of score but the players, I thought, pulled themselves together, pulled it round a bit and showed some character.’

Asked if this served as a reminder of how far Celtic have to go in order to get back to being competitive in Europe, O’Neill added: ‘Oh of course, absolutely. I couldn’t agree more, you’re right.

‘This is, European football is where this club, because of the great Jock Stein, has been a priority, but tonight there, it can show you. We have to get to that stage again. We have to improve.’

Osmand was a bright spark for Celtic when he came off the bench at half-time, winning the penalty which Hatate scored and looking lively.

But the 19-year-old striker was cruelly stretchered off in the closing stages and O’Neill confirmed he will now be set for a period on the sidelines.

‘He’s pulled the hamstring and that’s something that obviously, he’s very young, it’s never happened to him before,’ said the 73-year-old veteran boss.

‘So he doesn’t know and yeah, he was distraught because I think the reason being he was just trying to get his career going.

‘But if everything looks out well, he’ll recover from that and then start again. That’s what I’ve said to him, don’t do this.

‘You will certainly get going, this is just a setback for you but it’s not terminal in that sense and you can fight back, you’ll be out for X number of weeks now. It is a shame because he was trying to make an impression but that’s it.’

Sitting on four points with four games remaining against Feyenoord, Roma, Bologna and FC Utrecht, Celtic face an extremely tall order to qualify for the knockout stages.

But, insisting that it’s not yet over, O’Neill added: ‘I probably always thought this here that 10 points would probably get you, so we’re not out of it.

‘That’s a big lesson for us to know, to know what it takes to be a really decent European team. Midtjylland are a fine side and they deserved to win tonight.’