Celtic boss Martin O’Neill admitted his side were ‘masters of their own downfall’ in their sobering 4-1 Europa League play-off round first-leg defeat to Stuttgart.

Bilal El Khannouss netted either side of a Benjamin Nygren strike in the first half to put the visitors in command, with Jamie Leweling and substitute Tiago Tomas adding gloss to the scoreline late on.

It leaves O’Neill’s men with a mountain to climb in Germany next Thursday, and the 73-year-old — who marked his 1,000th game in the dugout last night — was under no illusions regarding the task at hand.

‘It’s a tough evening for us,’ he told TNT Sports. ‘On paper, 4-1 looks pretty poor but we were masters of our own downfall in many aspects.

‘We conceded poor goals. At 1-1 we were well in the game, even at 2-1.

‘It’s a tough ask (to get through the tie). You’re travelling over to a side who are fourth in the Bundesliga and are very capable of winning this competition.

‘At some stage, Celtic will become a top-quality team, but that’s in the future. At this minute, our battles are elsewhere.

‘It’s very difficult for Scottish teams. There’s no money. You’re talking about Premier League sides and Bundesliga sides buying players for £40million and them not playing.’

Goalkeeper Kasper Schmeichel was at fault for two of the goals conceded, with some fans booing the experienced Dane in the second period.

When asked if he would consider dropping the 39-year-old against Hibs on Sunday, O’Neill said: ‘Kasper Schmeichel has made some big saves since I’ve been at the club.

‘The game against Feyenoord, he pulls off a great save, and (without that) we may not even have been playing here.

‘This is a collective. I didn’t (hear any boos). I genuinely don’t know.’

Supporters staged a protest against the board within seconds of the first whistle, with stewards and players tasked with clearing tennis balls thrown from the stands on to the pitch.

The manager believed that had an adverse effect on his side in the early stages. He said: ‘Anyone who thinks that is a good idea needs their head examined.

‘A way back, this was an incredibly difficult, intimidating place to come. Teams like Juventus were terrified coming here.

‘That sort of thing does not help at all. What it does do, is Stuttgart find out there’s a lot of infighting going on. It doesn’t make sense to me.

‘If I’m a Stuttgart player, I’m pretty happy if that’s the case.’

Captain Callum McGregor admitted Celtic will go to Germany with little other than pride to play for.

‘I think they scored at good times,’ he said. ‘I don’t think it’s a 4-1 game and if you look back, we had some good moments.

‘The goals come at good times for them and kill any of our momentum. I think the third goal is the one which kills us.

‘We have to keep going, have to keep fighting, so many big games. That won’t define the season in terms of what we’re trying to do.

‘The focus is now on Sunday (against Hibs) and when we go there (to Stuttgart) next week, we have to claw some pride back.'