Kristoffer Ajer is one of the Celtic stars who’s left Neil Lennon fuming with his attitude behind the scenes, Football Insider understands.

The Hoops manager came out firing in his post-match press conference after the Champions League exit to Ferencvaros last night told his wantaway players to quit if they do not want to be at Parkhead.

Lennon did not reveal the identity of the players causing him angst behind the scenes.

But a well-placed Celtic source has told Football Insider that giant centre-back Ajer is one of those keen to secure a transfer before the window shuts in early October.

The Norway international, 22, has been targeted by Premier League and top Italian clubs this year.

He went public with his desire to quit – via his former agent – but speculation has quietened after Celtic slapped a £20million asking price on him.

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The Scottish giants have made a number of attempts to tie Ajer to a new deal to replace his current agreement, which expires in 2022, but he has rejected them.

The defender is believed to be among those who Lennon was thinking of when he let rip after the 2-1 home defeat to Hungarian champions Ferencvaros last night.

Lennon said: “Get your mentality right, get your attitude right. If some of you don’t want to be here, leave.”

Asked if he believed some players did not want to be at the club, he responded: “In some cases.”

Ajer has developed impressively over the last two years and established a strong centre-back partnership with Christopher Jullien as Celtic swept all before them last season.

The Norwegian started alongside Jullien in central defence last night after being surprisingly left on the bench against Dundee United and KR Reykjavík in the previous two matches.

In other Celtic news, club has responded to big-money Hoops offer for defender ‘desperate’ to move to Parkhead.