They may not have been capable of buying a win away from home, but under the floodlights at Celtic Park they were likely to surprise anyone. Nowadays they still toil on foreign soil – that victory over Dynamo Moscow in August remains something of a one-off – but the magic dust of indomitability seems to have been blown furth of G31.

Tony Mowbray’s side badly need to take something from their Europa League match against Hamburg in Germany this week. But Mjallby, now a pundit on Swedish television, is in no doubt that his former club’s problems this season have arisen largely from their inability to close out games at home, either in domestic competition or in Europe. On Saturday they knocked three past Kilmarnock to give themselves a much-needed confidence boost going into Thursday’s encounter at the HSH Nordbank Arena, but already this campaign they have dropped points at Parkhead to Dundee United and Motherwell in the SPL, been knocked out of the League Cup there by Hearts and failed to record a solitary win at home in European competition.

“The most worrying thing this season for Celtic is that their home form is not what it used to be,” Mjallby said. “Even when very, very big teams came to Scotland in Europe a few years ago, you couldn’t really say who was going to win – usually we were the favourites, and that’s not the case any more.”

Things have undoubtedly changed off the park since then – for a start, Celtic no longer have the spending power Martin O’Neill benefited from as manager. Chris Sutton, remember, cost £6m alone. But Mjallby was insistent that the team currently sitting bottom of Europa League Group C are capable of turning things around in their three remaining matches.

“They probably need a win in Hamburg and it’s not going to be easy,” he said. “But I think at Parkhead in the last game Celtic played pretty well. They didn’t create a lot of chances, but the energy was there and they competed well. Hopefully they can create a little bit more in Germany, and with a bit of luck they can snatch the three points.”

In the event, Celtic were undone by a Marcus Berg goal in the 63rd minute in Glasgow the other week. The 23-year-old former Gothenburg striker, now a regular for Sweden, is a player Mjallby has been aware of for some time and though he expressed some reservations about his overall work-rate, he warned that the youngster may be an even greater threat playing in front of his home crowd.

“I saw a bit of him when he was breaking through at Gothenburg, and then he went to the Dutch side Groningen and now he’s obviously taken a big step up signing for Hamburg and playing in the Bundesliga,” said Mjallby. “Obviously it’s going to be harder for him, but hopefully it’ll be good for him as well.

“I’ve seen him a few times for Hamburg and in the game at Parkhead, and he played surprisingly well in Glasgow. He has always been good in the penalty box – he’s a good goalscorer but outside the box he’s never really impressed me until now. He always seemed to be a bit hot and cold. But in Glasgow he controlled the ball, he played well as the target man and he’s gaining confidence so he’ll be even harder to play against in Germany I think.”

At Groningen, Berg scored 33 goals in just 56 appearances and was also being chased by Tottenham before signing for Hamburg for a fee of €10.5m in July. It was anticipated he would be used sparingly and given time to adjust to life in the Bundesliga but injuries to Paulo Guerrero and Mladen Petric have meant he has taken centre stage earlier than he may have bargained for.

“When they signed him I think they thought he would take some time to develop in order to show his true qualities,” said Berg’s countryman. “But obviously with the injuries he’s had to step up and he’s done very well. With time I think he’s going to be even better, and for Sweden with Henrik [Larsson] retiring, he’s one of the names in the hat to really establish himself when the new manager comes in.”

It remains to be seen who will be tasked with containing Berg on Thursday night. Stephen McManus, Gary Caldwell and Glenn Loovens are all fit for Celtic, leaving Mowbray with a decision to make as to who to leave out. Mjallby – a mainstay alongside Joos Valgaeren and Bobo Balde of an incredibly solid Celtic defence in the O’Neill era – refused to indicate which pairing he would prefer to see, but said: “There’s always going to be times when you have problems in a particular area of the park. The only thing you can do to get it right is to do it on the training pitch and make sure you have a leader in the back four – a guy who has a bit more responsibility and acts as the manager’s voice out on the pitch.”

By whatever means, Mowbray needs to make an imprint soon.