Martin O’Neill did not hide his anger after Celtic’s defeat to Stuttgart, but his frustration was not aimed only at what happened on the pitch.

The Europa League tie was halted inside the opening minute after objects were thrown onto the park in protest. It set the tone for a tense evening. Celtic went on to lose 4-1, leaving themselves with a mountain to climb in Germany.

There is context to the anger in the stands. A section of supporters feel ignored by the board. The Green Brigade remain banned. Transfer dealings and the direction of the club have been questioned for months. For some, the protest was the only way to be heard.

O’Neill, though, was focused on the timing. He has managed big European nights at Celtic Park before. He knows what a hostile atmosphere can do to visiting teams. On this occasion, he felt it worked the other way.

He said: (TNT Sports), “Anybody who thinks that’s a good idea needs their heads examined. There’s no question about it. Needs their heads examined.

“First of all, it sends out the totally wrong message. We’re playing against Stuttgart. The game is hard enough and they’re coming here.

“And the problem is that way back some years ago, this was an incredibly intimidating place to come to. Incredibly difficult. I’d managed here where sides like Juventus were scared stiff of coming here, where top class sides were scared stiff.

“That sort of thing does not help at all. There’s battles going on. Understand all sorts of things really.

“But that doesn’t help because what it does do, Stuttgart here, who might be, you know, to come to this wonderful football club and then find out that there’s a lot of infighting going on and things being thrown onto the pitch at the end of it all, doesn’t make any great sense to me.

“It’s just, you know, if that’s the case, because what it does, if I’m a Stuttgart player, I’m I’m pretty happy in this environment then, if that’s the case.”

O’Neill’s point is clear. When Celtic Park loses its edge, opponents grow in confidence. Stuttgart settled quickly after the delay and took advantage of defensive mistakes.

At the same time, the frustration among supporters did not appear overnight. Results have dipped. Recruitment has been debated. The ban on the Green Brigade has altered the feel inside the stadium.

Both things can be true. Fans have the right to voice concerns. A manager preparing for a European tie wants unity behind his players. On a night when Celtic needed every advantage, the split mood was hard to ignore.