First-leg strikes from Kris Commons and Giorgos Samaras in Sweden last week put Celtic FC on the cusp of UEFA Champions League qualification, but as the Hoops prepare for Wednesday's visit of Helsingborgs IF, Charlie Mulgrew urged his team-mates to shake off any creeping complacency.

"We don't think about being 2-0 up," Scotland defender Mulgrew said. "We'll go in to win the game and hopefully we can do that. Of course, it will be in the back of our mind somewhere but we've got to try and forget that and go out to do our job."

The 26-year-old believes that manager Neil Lennon's preparations have left the squad well-positioned to do precisely that in their play-off second leg: "Nobody in that dressing room thinks the tie is done – not at all. The manager has drilled that home to us. We can't get complacent. It's still only half-time and there's a long way to go."

With the prize on offer a group stage berth, Mulgrew needs no reminders about how important the match in Glasgow is, and says there is only one way to approach the contest. "This is probably the biggest game of my career," the former Aberdeen FC man said. "It's massive for the club and all involved. If we get there, I'm sure we can compete and not just make up the numbers."

Lennon's side are close to making the tournament proper for the first time since 2008/09 and the manager is sweating on the fitness of several players. "We still have a few nagging doubts," he said. "Thomas [Rogne] has an ankle problem, Kris [Commons] has an ongoing ankle problem and Scott [Brown] has a sore groin. Apart from that, we have a decent-sized squad to pick from."

Lennon's Helsingborg counterpart Åge Hareide saw his team suffer their third straight defeat on Saturday, 3-1 at Djurgårdens IF in the Swedish top flight, yet despite the deficit they face against Celtic, the visiting coach feels they have plenty to fight for.

"We are optimistic," he said. "I have never lost in Scotland as a manager and I intend to keep that record. Football is about belief and we really believe we can do it. It is about seizing the moment and this could be a once-in-a-lifetime chance for some of our young players. To come here and play at one of the best grounds in Europe, in front of the best fans in Europe, must be a fantastic inspiration."