The Scottish champions’ hopes of reaching the last 16 of the Europa League were crushed by Zenit St Petersburg, who overturned a 1-0 first-leg deficit with a comprehensive 3-0 victory at the  Krestovsky Stadium.

It was Celtic’s heaviest Europa League or Uefa Cup defeat since an ignominious 5-1 loss at Neuchatel Xamax in 1991.

It left Rodgers lamenting his team’s approach to the match, along with some wretched defending which contributed to goals by Branislav Ivanovic, Daler Kuzyaev and Aleksandr Kokorin for Zenit.

Zenits Aleksandr Kokorin celebrates scoring his sides third goal as Mikael Lustig and Celtic keeper Dorus De Vries are left stranded. Picture: AP.

The Celtic manger said: “Defensively, we lacked aggression, particularly in the first half. We didn’t close the space quick enough. We talk about defending forward and we just didn’t defend forward well enough. We conceded poor goals from that.

“The first goal from a corner is one that can happen. We were blocked off, Zenit worked it well and found the space – Branislav is outstanding in the air. The second goal, we didn’t engage quick enough from a throw-in. We’re too deep and have to press the guy who was shooting.

“At 2-0, we still have an opportunity in the game. But everything was too sideways and backwards. That’s about bravery and having that courage to play.

“With so many young players in the team, you see the contrast from last week. We started the second half okay but, again, we concede possession too cheaply and they work the ball round for a cross. We should never concede that type of goal.

“We were much better than Zenit in the first leg. If we played with a little bit more courage and belief tonight, we could maybe have got a result.”

Rodgers has led Celtic to the group stage of the Champions League in two successive seasons but admits they remain a long way short of the standard required to make significant further strides in European competition.

“There is still an awful lot of work for us to do,” he added. “When I take a step back, there have been a lot of positives for us in Europe this season. We have played very well in some games, shown some great qualities.

“Of course we are up against the best of the best. So there is a lot of learning taking place. It’s about consistency, really. Last week was an outstanding performance which would allow you to think you had a great opportunity to go through but if you don’t start with that aggressive mentality, then it’s really difficult.

“Over the course of both competitions in Europe, there have been aspects which pleased me. We are taking steps forward with a lot of young players. We now have to finish our domestic campaign as strongly as we can and create another piece of history on that front. We then need to look to take another step forward in Europe next season.”

Zenit head coach Roberto Mancini was understandably content with the turnaround in his team’s performance level after having been outplayed in the first leg.

“We deserved to win,” said Mancini. “We played a very good game. Celtic are a strong team but we played very, very well. Celtic’s tempo in Glasgow was very difficult for us. Tonight we scored three goals, had other chances and for 75 minutes didn’t concede any chances to Celtic.”

Brendan Rodgers: Celtic weren't brave enough