Celtic right-back Alistair Johnston knows they must take lessons from his most difficult night in football to ensure it was not a wasted evening.
Johnston feels their performance in a 6-0 defeat by Atletico Madrid was unacceptable despite losing Daizen Maeda to a VAR-assisted red card midway through the first half.
Celtic trailed 1-0 when the Japanese attacker was sent off and Atletico exploited the numerical advantage with the help of three spectacular second-half goals.
Manager Brendan Rodgers persisted with a 4-3-2 formation, but Celtic could not get the ball forward to their two strikers.
Johnston said: “The red is obviously frustrating, but at the same time there’s mistakes all around from us, in all the matches, all the goals we conceded, personal, small individual ones.
“And the quality is just so good. Some of the finishing you look at and it’s unbelievable. But that’s what this level is all about.
“We need to clean that stuff up. It was a difficult performance all around. Certainly for Celtic, but in my professional career I have never had a game like that where they do whatever they want to you, almost.
“It’s frustrating, it’s difficult, because you can’t get on the ball and it feels like you can’t get in their half and create anything, it’s just wave after wave.
“And that’s something we are going to be disappointed with because, even after we go down to 10, as difficult as that is, it doesn’t mean that we should concede that much territory and possession and that many opportunities.
“We have to look at ourselves in the mirror, individually and collectively, and really figure out what we want to do there because it’s unacceptable.”
Celtic have generally been competitive in their Champions League campaign, but three red cards in four games have taken their toll.
Johnston said: “If you don’t take anything away from it then it’s really a wasted night. No matter what, win or loss, you have to look back on every match and try and take something positive out of it to grow as a group.
“Again, this is a really talented team, they have World Cup winners littered through that squad, and they punished us.
“We can all see what the level is, what the level is like. We have to look back on it with unbiased eyes and opinion because, although they were at a different level, there were some easy things that we can clean up on.
“We played with nine men at Feyenoord and we looked more solid. Obviously this was a longer period but I think we made it a little too easy, we were too passive. We could have shown more as a group of 10 men, we felt like we could have dug our heels in more.”
The defeat left Celtic on one point at the foot of Group E, but they can still qualify for the last 16 if they beat Lazio and Feyenoord and hope that Atletico do them some favours.
Johnston said: “We need a response against Aberdeen on Sunday and there’s still something to play for in this group.
“We have put a lot of pressure on ourselves to get three points against Lazio, and if we do that we give ourselves a chance.
“We have put ourselves in a difficult position, but I don’t see this scarring us.
“We have a strong enough leadership in this team that we will be able to push this behind us, but we need to take something positive from it to grow.”
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