Outside hundreds of fans loudly vented their frustration.
As cries of "sack the board" assailed the marquee that served as the zone for press interviews, Callum McGregor, the 21-year-old Celtic midfielder, spoke of the silence in the dressing-room after the 1-0 defeat by Maribor which condemns Celtic to Champions League exile.
"It's just devastating. It's a really tough one to take," said the midfielder, who was one of the few successes on a night of widespread under-achievement in Celtic ranks. "The dressing room was silent at the end. We couldn't believe it. In the second half, we had a few chances but then we got sucker-punched at the other end. It's such a hard one. The feeling now is a mix of everything - anger and frustration."
A newcomer to the team, the player was in no doubt as to the significance of the defeat to the Slovenian champions. "The Champions League was massive for the club. But it also meant everything to all the staff and the players. It is a huge disappointment that we will not have it this season," he said.
"We will just have to work hard to try and get better. We will look to get better over the course of this season and come back and try and qualify next season."
Celtic were never controlled or composed as a huge crowd roared for a result that would allow the club to progress to the group stages. "Were we edgy? It felt like that a wee bit. They were happy to sit in and defend and that made it difficult for us to try to break down. Once they managed to get a few shots on target the crowd start to get on your back a bit and it becomes difficult.
"We threw pretty much everything we had at them and we were unlucky at some points. Virgil [van Dijk] had a couple of efforts and I had one that hit the bar. You can say we were a wee bit unlucky there but you have to defend well at the other end as well. We conceded a sloppy goal and that cost us."
That goal from Tavares means Celtic go into Friday's draw for the Europa League after the 1-1 draw in Slovenia made them favourites from the group stages in the Champions League. "We had an advantage from the first leg and I think everyone expected us to go through tonight," admitted McGregor, who was called up for the national team this week.
Asked if the Europa League was the best level for the team now, he conceded: "Maybe the Europa League is a stepping stone for us to get better as a squad and come back stronger next year."