Former Celtic assistant manager Murdo MacLeod says the players are hurting after the Champions League defeat by Aalborg ended their European dream.
"The Uefa Cup was there for Celtic last night and they threw it away in the last few minutes of the game," MacLeod told BBC Sport.
"The Danes are no better than a SPL bottom-of-the-league type club. I don't think they'll get far in the Uefa Cup.
"The big problem has been that Celtic haven't scored enough goals."
Defeat in Denmark means Celtic will finish bottom of Champions League group E and also miss out on the Uefa Cup spot, which Aalborg secured with their dramatic 2-1 victory.
And MacLeod, now a BBC Scotland football pundit, said Celtic would rue the missed chances and the defensive mistakes that continue to haunt them away from home in Europe.
Two points after five games for Celtic has got be viewed as a really poor campaign
Murdo MacLeod
"If you've had 18 games away from home and only drawn once, then I think you can say there's something wrong. But, there are a lot of new players who have come to Celtic in the past couple of seasons," he said.
"They've enjoyed some great rewards and getting into the last 16 of the Champions League twice was a great achievement. But this time they got off to a bad start at home, then losing in Villarreal and losing at Old Trafford.
"Two points after five games isn't enough to qualify. It's got be viewed as a really poor campaign. Celtic aren't scoring enough goals, they're winning games for fun in the SPL and now they've gone out to a poor, poor side.
"I spoke to a couple of the players after the game and they're hurting about the quality of the side that they lost to. The Celtic players know they're a better side than Aalborg."
MacLeod said that Celtic manager Gordon Strachan would have expected his side to add to their lead after Barry Robson headed them in front.
"Celtic didn't see it coming last night. They were 1-0 up; very comfortable and looking for a second goal and all of a sudden it's 1-1," added MacLeod.
"I'm sure that, at some point, Gordon will think back and look at the changes he made.
"He changed Samaras, and I thought that was an easy one as Samaras had run out of steam. But, throughout the 90 minutes, I thought the team actually played well last night.
"However, when it went to 1-1, it let Gordon know that Aalborg could score goals and it hit a wee panic button."
MacLeod added: "I think Gordon should've looked at it and put Paul Hartley on and brought Gary Caldwell back into central defence. Maybe even have played five at the back.
"Gordon must have felt that Celtic would've gone on and got a second goal. But it wasn't to be and then Celtic scored one of the cruellest own goals you will ever see.
"There was no-way back with only a few minutes to go."
Celtic return to domestic duties on Saturday with a home game against Inverness CT in the SPL.
But MacLeod said the club would have to change if they are to make progress in the Champions League in future.
"Conceding goals is a major problem. When Celtic score away from home everyone gets a lift. And at home they think they can beat anyone.
"Celtic have to look at it across the back. They also need to think about how their midfielders and forwards are going to defend.
"If Gordon wants to take Celtic further in the Champions League, then he's going to have to spend more than he has done in the past few seasons."
Murdo MacLeod was talking to BBC Scotland's Annie McGuire on Sports Report
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