Celtic must strive to make an impact in the Champions League and not be content with simply taking part, says former skipper Paul Lambert.
Manager Brendan Rodgers spoke on Monday of his players "growing at this level" and "gaining invaluable experience".
Lambert was a Champions League winner with Borussia Dortmund in 1997 before spending seven seasons at Celtic.
"I don't think you learn in the Champions League, you have to hit the ground running," he told BBC Scotland.
"It's too big a competition to say you are learning all the time.
"Yes, you might get the experience but I think you're trying to make a mark in it and to do that you have to be performing at the top of your game.
"Celtic have done great to get to the Champions League but there has to come a point when you say you can't keep learning all the time - you have to make a mark in it."
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Celtic host Bayern Munich on Tuesday, having lost 3-0 to the Bundesliga champions in their last Group B outing.
The phase began with a crushing 5-0 home defeat to Paris St-Germain, which was followed by a heartening 3-0 triumph away to Anderlecht.
Defeat to Bayern in Glasgow would end Celtic's hopes of progressing to the last 16.
Rodgers has spoken often of his refusal to compromise on an attacking style against top level opposition.
"It's my job to convince the players we can go and play how we want to play, as opposed to sitting back," the manager repeated on Monday.
Lambert, 48, led the Celtic side that reached the 2003 Uefa Cup final and enjoyed several memorable European nights with the Scottish champions.
"At any big club, the fans expect you to be on the front foot," he said.
"You have to be really concentrated and disciplined. When you defend, you have to do that really strongly as a team. You can't come out and leave gaps or you'll get hurt.
"But, by the same token, you have to get on the front foot and try to win because the fans will demand it.
"It doesn't matter who comes to Celtic Park, the fans' level of expectancy is huge."
Bayern are without star forwards Robert Lewandowski and Thomas Muller for Tuesday's match but Lambert is impressed by the visitors' squad depth and a defence that has conceded just one goal in five games since veteran manager Jupp Heynckes returned.
"They are big players but I'm not so sure they will be missed," he said. "Bayern are still a top, top side and have players who will thrive on the atmosphere.
"They have one of the best back fours that I've seen in a long time. Jerome Boateng and Mats Hummels are excellent in their build up play, Joshua Kimmich is a terrific young right-back and David Alaba is right on top of his game."