After being eliminated by unfancied Kazakh side Kairat Almaty in last season's play-offs, Celtic endured an even more painful exit on Tuesday, throwing away a four-goal aggregate advantage against Austrian champions LASK. A 5-1 defeat on the night saw them lose the tie 5-4 overall.
Celtic face fallout from Champions League collapse
Scottish champions Celtic are facing a second consecutive season without Champions League football, a setback manager Martin O'Neill admitted will have major financial consequences and could also make it harder to attract new players.
Missing out on the league phase is expected to cost Celtic around £40 million ($55 million), although they will have the consolation of competing in the second-tier Europa League.
O'Neill, now in his second full-time spell with the historic club after guiding Celtic to the title on the final day of last season with a dramatic victory over rivals Hearts, acknowledged the scale of the setback.
"The qualification for the Champions League is major, it's major in every aspect," said the 74-year-old Northern Irishman.
"Financially, for prestige, but we have to pick ourselves up. That's my responsibility again to do that.
"I think I said last week that if you could qualify for the Champions League there would be players wanting to come on that basis.
"That's not going to be the case."
O'Neill, who won the European Cup twice as a player with Nottingham Forest, also conceded that Celtic's squad requires strengthening after the defeat exposed their shortcomings.
"We know that we are a million miles from the finished article," said O'Neill, who led Celtic to the 2003 UEFA Cup final during his first spell in charge.
"That's absolutely true. I think we thought that anyway."
- 'Suck it up' -
O'Neill, who missed the beginning of the domestic campaign after undergoing a hospital procedure for a "couple of ailments rolled into one", was more measured in his assessment than captain Callum McGregor.
The 33-year-old midfielder, who has spent his entire career at Celtic apart from an early loan spell with English side Notts County, delivered a far more critical verdict.
"We got what we deserved," he told Amazon Prime.
"We were passive all night. We looked scared to go and win the game.
"I didn't think we were that good in the first leg either. We scored at good times and got away with it.
"We have to suck it up. We apologise to our supporters and the club because there's no way we should lose that game."
While O'Neill accepted full "responsibility" for the disastrous display, McGregor insisted the players also had to shoulder the blame.
"It's as much on the players as everyone else. You can't look for excuses elsewhere," he said.
"You'll now see what people are made of. When you play like that you can't have any excuses whatsoever.
"When you go 1-0 up in the game and it still doesn't settle you, that is on us."
McGregor added that the response to the defeat would now provide a test of the players' character.
"You fall at a big hurdle and these questions are going to be asked. You can't lose by that margin then look for excuses elsewhere," he said.
"You have to bounce back, you have to show a reaction and that's what Celtic are all about."
Celtic's first chance to respond comes on Saturday when the Premiership leaders, who have six points from their opening two matches, host Falkirk, who have collected one point.
