KRISTOFFER AJER didn’t get a sniff of the Champions League this season and now he’s Celtic’s first choice central defender.

There are a number of factors at play here. Injury to Dedryck Boyata and Jozo Simunovic’s worrying loss of form have seen this 19-year-old become so important going into Thursday’s Europa League second leg against Zenit St Petersburg in Russia.

It would be wrong, however, to dismiss how well this young Norwegian, who arrived as a midfielder, has done at the heart of Celtic’s defence.

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Ajer has been a real success story of the past few months and given his age and position he now plays, is only going to get better and he’s made a decent fist of his first game as a centre-half.

“It wasn’t frustrating for me not to play in the Champions League group stages,” insisted Ajer. “I’m 19 years old. I need to take my chances when they come along. I feel I’ve learned a lot from the gaffer and the rest of the staff both in training and in the games I’ve played.

“I think I’m developing every single day. I didn’t think I’d develop quite as much as I have done this year but it’s a great feeling. I’m getting more and more games. With each one, I feel stronger.

“I just played my normal game against Zenit. The whole squad played with confidence. That makes it easier for a centre half to do their job.”

Ajer and Simunovic had their best game as a partnership last Thursday in the first leg. It is hard to shake off the feeling that they will need to be even better in the return when Zenit will have to attack more.

The back five worked and there is every chance Brendan Rodgers will go with that again; Mikael Lustig making up the three in the centre.

“Last week was a great result,” said Ajer. “To get a clean sheet at Celtic Park before the game in Russia was important as well. It’s put us in a strong position.

“We limited them to few chances. They’d one big chance in the first half but Dorus De Vries pulled off a fantastic save. Other than that we avoided giving away too much. That’s important for our confidence.

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“We’ve worked on the back five and lot and have played that system in different games. The gaffer gives us a really clear plan in terms of how he wants us to play and perform in that formation. So, it’s easy to get an idea of how we are supposed to play. It was good to perform like that.”

Ajer didn’t buy the theory that his Russian opponents were rusty after the best part of two months off courtesy of European football’s longest winter break.

“To be fair, I don’t think they were rusty at all,” he said. “I felt we pressed the game really well. They gave us a really good fight.

“It was just that we played very well. We were up for the game. It was a great performance and we deserved to win but we know they can hurt us in St Petersburg."