BRENDAN Rodgers was joking. Probably. Hopefully. When asked who he would fill in at centre-half as he deals with what in football terms is a defensive crisis and in the real world a case of a bit of tweaking, Celtic's manager dropped the name of James Forrest. Gallows humour and all that.

The winger has hardly put a foot wrong for a year and a bit now and if anything looks even sharper after the summer. However, Billy McNeill he is not.

Rodgers has problems at the back for the visit of Rosenborg on Wednesday in the second round of Champions League qualifying with Kristoffer Ajer and Jack Hendry his only recognised central defenders up to speed and available.

Mikael Lustig has now returned to Glasgow after being given time off after the World Cup. The Swede is an experienced campaigner but it would asking a lot of him to play after a couple of days light running.

Dedryck Boyata remains on holiday, Marvin Compper is injured and word around the campfire is the coaches and players have not been impressed by the German who has managed one game since joining in January. He might as well not be there.

And then there is Jozo Simunovic, a man skating on the thinnest of ice. Rodgers was far from impressed by the Croat’s awful display at Tynecastle last season when Hearts won 4-0, and since then red cards at Ibrox and against Alashkert last Wednesday which counts him out of the next tie – both needless – might mean he is on, or nearing, his last chance.

Celtic always felt a little light in defence. They have money to go out and spend £8 million on an experienced centre-half but would such a player choose Scottish football unless he was guaranteed to play in the Champions League? Celtic would want him in now so they could get to the group stage.

Who would have thought a year ago that Nir Bitton would be missed as at least he can play in defence, albeit it is far from his natural position.

Hendry has done fine but just being fine doesn’t get you to Madrid, Manchester or Munich. Celtic look a strong, exciting and attack-minded unit but as last season’s European campaign showed, teams must be able to keep clean sheets or they are in bother.

“Over the couple of years I’ve been here, this stage of the competition has always been tough for us,” Rodgers admitted. “We’ve had players out, especially centre-backs. But touch wood we get to this first leg and the weeks after that in good health.

“I’ll play James Forrest there! We’ll have a look at what to do with Lustig and Boyata. Compper I don’t think will be available. He got injured in training the other day and I’m not so sure he’ll be ready. We’ll just assess it and see where we are with the squad. We’ll see where the players are and take it from there.”

Ajer is a big positive but even he is raw and prone to mistakes, which is natural for such a young player still learning a position he took up only two years ago.

“Kris has had lots of experiences now,” said Rodgers who has great belief in the Norwegian. “Some good ones. He’s made big steps. He’s still only 20 but he’s really dominant. You always think that everything that comes through the middle of the pitch, he’s going to get his head on it.

“The speed of his passing is also getting better. He’s a natural leader as a young guy and is improving all the time. He was thrown in last year but a year later he’s a Norwegian international, a Treble winner and he’s developing really, really well.

“His rampaging runs from defence are part of how we build the game from behind. It helps when you've got someone of that quality. But it depends where the space is.

“If you're playing against one striker, the space is on the outside with the two outside centre-backs. But if it's against a two, the central guy like Kris has the space to go forward. When he attacks and steps in, he breaks lines very well.

“You get players like that. They find themselves on the edge of the box – but the problem is, they have to get back. I remember Gerry Taggart doing that for Leicester. He used to step forward and just barge everyone out of his way.

“Kris is very elegant and the comfort he feels with the ball is very important. I need that with all of the players. We need that to pass and play the way we want. But it's really important that they can defend as well. Will other clubs look at him? I've no doubt because he's a young central defender who can play.

“But first and foremost you have to be able to defend. Kris doesn't take many risks, which is the key point. He's come from Norway where he played as a number 10 scoring goals, to developing as a centre-half. He has to be able to defend, first and foremost. But if you can build up play as well, you can be critical for the team and how we play. Kris is very comfortable at that.”

Rosenborg are not the team they once were, even from 12 months ago, and the strange situation with the manager is hardly going to help.

“They’ve had a few changes,” said Rodgers. “How Rosenborg set and play is exactly the same and it’s been that way for a number of years. They go 4-3-3 and try to work the ball.

“They’ll be pleased they got through the tie against Valur, scoring late on. Any game at this stage is always tough so we’ll look to prepare and get ready for the two legs. We’ll look to take an advantage from the first leg on Wednesday.”

Rodgers will also hope to have a few more of his big men on the plane to Trondheim for the return next week.