BRENDAN Rodgers last night stressed it will require “big money” to strengthen his Celtic squad - and admitted he is unsure if he will be able to improve the double treble winners before the transfer window closes.

The Glasgow club, who take on Rosenborg in the first leg of the Champions League third qualifying round at Parkhead tonight, spent a club record £9 million on Odsonne Edouard last month.

But their attempts to sign John McGinn from Hibernian have proved in vain and they had a £2 million offer knocked back earlier this week.

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And they will field an inexperienced defence against their Norwegian opponents due to the absence of key players Dedryck Boyata, Mikael Lustig and Jozo Simunovic.

Rodgers is keen to qualify for Europe’s premier club competition for the third season running and make a major impression in it.

But asked if he thought his Celtic squad would be better when the transfer window closes next month, he said: “I’m not sure. The problem is that if you are going to bring in a top, top centre-half then that is going to cost you money. It is as simple as that. And big money. That is out of my control.

“We can’t do it. The club works in a specific way. You don’t need to be a rocket scientist to know that if you are going to improve drastically from where this group is at and where it has got to over the last couple of years and make the improvements that people want to make, it costs money. But that is out of my control.

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“You have to do what the club has always done. You bring in players who fit the model of the club and you develop them and improve them and then probably eventually they move on. Somewhere along the line you’ll need that level of experience to come in and try and support and then you hope that can work out for you.”

Meanwhile, Rodgers has stressed he is keen to hold onto Boyata, who impressed for Belgium at the World Cup, and emphasised there was no prospect of the defender moving on while Celtic can still qualify for the Champions League.

“He’s got a year left on his contract,” he said. “He’s done well in the last 18 months for us and did well at the World Cup, so naturally there’s going to be interest in him.

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“We don’t want to lose him, he’s a very valuable player for us, but if he doesn’t sign his contract then he goes on to another club. That’ll be up to him in the end.

“But at this point in time he’s very important for us to help us achieve our goals early on in the season.”

Rodgers added: “I’m not sure there’s an offer that would make us even think about it because of the stage of the season we’re at. We’re playing very important games that can set us up for the season. We need our best players available for that and he is clearly one of them."

Meanwhile, Rodgers, who will be missing Moussa Dembele and Leigh Griffiths for the Rosenborg game tonight, revealed that he had feared Edouard would miss out as well.

"Edouard had a swollen knee after the Alashkert game and didn’t train until yesterday," he said. "Moussa is probably a good couple of weeks away. He’s come back so fit and strong."

Rodgers won't rush Lustig, who returned to training Monday, back for this game, but confirmed that Tom Rogic was available for selection. He also revealed that Jonny Hayes and Leigh Griffiths will return to training after lay-offs on Thursday.