Celtic's hopes of Europa League progress are all but over after a 4-1 thrashing at home by Stuttgart in their knockout play-off first leg.
Martin O'Neill's side now have a monumental task to turn this tie around in Germany next week and progress to the competition's last-16. But while their Europa League hopes were crushed on the pitch, Thursday also saw fractures around the club glaringly exposed.
The game was halted just seconds after the first whistle as Celtic fans threw tennis balls onto the pitch in protest at the club's board. By the second half, they were booing their own goalkeeper Kasper Schmeichel. At the end, only a few were left to vent their frustrations.
Tiago Tomas' injury-time fourth looks to have all-but ended this tie as a contest but, throughout, Celtic were second best.
Schmeichel should have done better with El Khannous' first strike, having kicked off a serious of errors from Celtic with a poor pass out from the back. He then failed to keep out a similar low drive from the edge of the box from Jamie Leweling for Stuttgart's third.
But the defenders in front of Schmeichel also endured a torrid night, giving El Khannous too much space to head in his and Stuttgart's second, while a VAR call for offside prevented Ermedin Demirovic from registering a fourth. Tomas eventually did so, after just failing to reach a close-range header moments earlier.
Stuttgart - fourth in the Bundesliga - finished 10 places above Celtic in the league phase and looked a class apart all night - aside from a brief lapse from captain Atakan Karazor, which allowed Benjamin Nygren to briefly level it up.
Celtic had scored stoppage-time winners in their previous three fixtures but the sight of Julian Araujo - the 97th-minute match-winner at Kilmarnock on Sunday - sliding a huge chance wide in the final seconds, summed up the performance.
This was the first defeat since O'Neill's latest return to Celtic, on the occasion of his 1,000th game as a manager. It was a brutal wake-up call as to where Celtic are at.
Celtic boss Martin O'Neill to TNT Sports:
"It's a tough evening for us, obviously, 4-1 looks pretty poor. We were masters of our own downfall in many aspects. We conceded some very poor goals.
"I felt at 1-1 we were well and truly in the game, even at half-time, 2-1 down. It was a tough evening."
On turning it around: "It's a tough ask. We're travelling over there, fourth in the Bundesliga, very capable of winning this competition, a good side.
"At some stage, Celtic will become a top-quality European team. That's in the future. At some stage or other. But at this minute, our battles are elsewhere. Our focus now is totally on Sunday."
Celtic captain Callum McGregor to TNT Sports:
"Everyone makes mistakes. Everyone has off nights. Kasper has been amazing since he came to the club, a really big part of the success, a big, big player in the dressing room for us as well.
"He'll dust that down and go again. Everyone is all-in together. We win as a team, we lose as a team.
"There's no blame or any of the players looking at him. He's made so many big saves for us and he'll bounce back, I'm sure."
