RONNY Deila was today told he has to stop tinkering with his defensive line-up if he wants goalkeeper Craig Gordon to rediscover his top form with Celtic in Europe.

Deila and his Hoops players will fly out to his native Norway tomorrow ahead of their massive Europa League meeting with Molde on Thursday evening.

Getting a result against the surprise Group A leaders away from home will boost the Scottish champions’ bid to progress to the knockout stages for the second season running hugely.

However, the Parkhead club’s displays at the back have often been far from impressive in continental competition during the 2015/16 campaign.

They let in four goals against Swedish champions Malmo in the two legs of the Champions League play-off and missed out on a lucrative place in the group stages as a consequence.

And they have let in two goals against Ajax away in Amsterdam and Fenerbahce at home in Glasgow in their two Europa League outings so far this term.

Deila has fielded several different players in his rearguard in those outings - including Efe Ambrose, Tyler Blackett, Dedryck Boyata, Virgil van Dijk, Emilio Izaguirre, Saidy Janko, Mikael Lustig, Charlie Mulgrew, Jozo Simunovic and Kieran Tierney.

The 40-year-old’s task has been complicated by the fact that first choice centre half Van Dijk was sold to English Premier League club Southampton in an £11.5 million transfer last month.

He has also been deprived the services of key first team player Mulgrew and new £5.5 million signing Simunovic due to injuries.

However, Celtic legend Pat Bonner believes he has to settle on his first choice defence if he wants Scotland internationalist Gordon to scale the heights of last season.

“Craig has done exceptionally well since he has come into the Celtic side after recovering from his injury,” he said.

“He has tailed off a bit this season – but that has more to do with the back four not being settled in front of him. For me, that is much more to do with it than him.

“In the main, Craig has been magnificent. Last season he certainly had a magnificent campaign. But his confidence has definitely gone down a little bit.

“But it is always difficult to build up relationships with your defence if it keeps changing. No matter who the goalkeeper is, if you don’t have a settled back four it does take its toll."

Bonner continued: “I think Craig has been very unfortunate this year. Last year he had Jason Denayer and Virgil van Dijk there in front of him. Between Craig and the two of them Celtic had a magnificent defensive record.

“But then it changes and they are trying to find who is going to be the best combination back there. It has taken time and that for me is why they have lost goals this year. That is always the case.”

Bonner takes a fascinating look back on the 17 years he spent between the sticks at Celtic in his newly-released autobiography The Last Line.

He reckons the fact that he knew who would be playing directly in front of him was crucial to the many league and cup successes he enjoyed during his distinguished playing days.

“Going back to when I was a player, at Aberdeen you had Jim Leighton, Willie Miller and Alex McLeish and at Dundee United you had David Narey, Paul Hegarty and Hamish McAlpine,” he said.

“At Celtic you had Tom McAdam, Roy Aitken and myself or Mick McCarthy, Roy Aitken and myself. We were fairly settled.

“The big teams down in England were exactly the same. You had Steve Bruce, Gary Pallister and Peter Schmeichel at Manchester United. It definitely benefits a team to have that continuity.”

Bonner continued: “If you have a solid back four then it makes the goalkeeper’s life much easier and they can then grow in confidence and start making good decisions.

“When the defence is constantly disrupted then it becomes a problem. I think that is what has been the issue with Celtic this season. You are never sure who is going to be playing there.”

Deila's reliance on zonal marking at corners and free-kicks has caused consternation among the Celtic support this season due to the number of goals his side has conceded at set pieces.

Bonner believes using a mixture of man marking and zonal marking will allow his former club to achieve the sort of consistency they are looking for that the back.

"For me, you need a bit of balance," he said. "Mick McCarthy didn’t like picking up. He was a big rugged centre half and wanted to go and attack the ball. But he got guys around about him to pick players up to allow him to do that.

"That is what you have got to get right. Whoever isn’t capable of heading has to do a job on the players who are going to attack the ball for the opposition. That, to me, is key.

"If you ask players in a certain zone to go and head it they will head maybe 60 to 80 per cent of the balls. But that still gives the opposition to the opportunity to score one or two.

“The key for me is not to let players get the run. It is up to the players. They have to stand up and become the leaders on the pitch. The manager can’t run onto the pitch and do it for them. They have to take responsibility for it themselves.”

Meanwhile, Bonner has predicted the Republic of Ireland can overcome Bosnia over two legs in the Euro 2016 play-off and claim a spot in the finals in France next summer due to their never-say-die spirit.

Martin O’Neill’s side pipped Scotland to third place in Group D earlier this month courtesy of a sensational 1-0 triumph over world champions Germany in their penultimate qualifier in Dublin.

Bonner, who won 80 caps for the Republic, starred for his country at Euro ’88 in West Germany - where his Man of the Match-winning display helped secure a memorable 1-0 victory over England.

The 55-year-old feels the work ethic of O’Neill’s charges will help them in the double header against a country placed 14 spots above them in the FIFA world rankings.

“It is going to be hard,” he said. “But Bosnia were probably one of the best sides we could have hoped to have got. We definitely have a chance.

“You can be sure they will be competitive. They have fought to the end in every game they have played. They got a couple of lucky breaks at the end of games, but that is down to keep going.

“That is Martin’s way. They have fought to the end and haven’t given up. We have lacked a little bit of creativity and a bit of guile at times, but we make up for it with heart. That is why we are there.”