The Champions League group stage – in Celtic's grasp for a week – suddenly feels in grave danger of slipping through their fingers. Cue audible anguish around the Parkhead stands and an increase in the collective blood pressure. The atmosphere would instantly, and vividly, transform. How would the Celtic players cope?
Some teams fold when the heat is on them like that, and before they know it they've let in another goal. Celtic's 2-0 first leg lead in this Champions League play-off was achieved with the help of some luck last week, given the number of chances created and unfinished by the Swedes, but it is reasonable to expect that the Scottish champions will play more impressively tonight. One of the tests which awaits them is neither physical nor to do with their ability, but will examine their mental strength. If they do concede the opener to the Swedish champions – Celtic have kept a clean sheet in only three of their six fixtures so far this season – can they keep calm and carry on?
"We don't even want to think about that, but I'm sure the boys would respond and be up for the challenge," said Charlie Mulgrew. "It's great to get the supporters behind us but we can't affect how they would respond. We need to concentrate on what we need to do."
Mulgrew represents a link to a period when Celtic regularly appeared in the Champions League groups, albeit his connection is tenuous. Now Scotland's reigning player of the year and one of the senior defenders the team must rely on to deny the Swedes tonight, Mulgrew was merely a member of the club's youth system when clubs like Juventus and Lyon participated in stirring nights in Glasgow. He performed the usual menial duties expected of the apprentices. "I was behind the scenes, working and cleaning the boots a couple of times. I cleaned the boots the night Lyon came to Celtic Park and Liam Miller scored that goal." Miller and Chris Sutton scored in a memorable 2-0 win in 2003.
"It was great to be in about it and to see how that great Celtic team went about things. To be involved now is really special. The manager [Neil Lennon] has instilled in us the winning mentality that great team [under Martin O'Neill] had – you can see that coming across when we play now. I think there are definitely similarities in the mentality.
"This could hopefully be one of the special nights at Celtic Park. It would be massive to be part of the team that gets back to that stage. Huge. Watching Celtic in the Champions League when I was younger was a brilliant experience and going to the games was a real inspiration. To be involved as a player now would be a dream.
"You can say we're so close but the manager has made us aware that we're only halfway there. We need to concentrate fully and be up for the game or we will end up in trouble. Helsingborgs looked a decent side, they carried a threat in the first leg and created a couple of decent chances, so that was a wake-up call for everybody."
Celtic have never failed to qualify after a first leg win away from home, although Lennon was a member of the team which won 3-1 in Amsterdam in the comparable stage in 2001 only to then go 1-0 down at Parkhead. There was no further scoring, and Celtic qualified, but the memory of that tie has crossed Lennon's mind in recent days even if he quickly dismissed its relevance. "I haven't thought about it too much: different times, different teams, different opposition. Losing the first goal is a possibility and something we have to factor into the preparations. We would have to react in the right way."
Lennon and his players are on the brink. He's had a turbulent two-and-a-half years in management, but having delivered a league title and a Scottish Cup, and brought some stability to their form in Europe, the obvious next stage is to see them into the Champions League group. Only Scott Brown and Georgios Samaras, of the current players, have experienced that with the club. It has been absent from the biggest stage since 2008.
"It would be a progression," said Lennon. "The remit last season was to win the league, and we did that. That was progress. The next progress would be Champions League football. We would look at it and say 'that's good, that's progress for the team, they're going in the right direction'.
"James Forrest is as exciting as you get in British football so we are blessed with young talent. I don't want to build them up and then let them fall flat on their faces, but we know we have a good team here. To take them on and enhance and develop them further, the Champions League is where you want to play."