The 19-year-old joined the Bhoys in 2016 from Start for a reported fee of £500,000. He was sent out on loan to Kilmarnock where he made a strong impression.
Ajer is primarily a central defender, but he can play in the holding midfield position as well. He has established himself as a first team regular in Brendan Rodgers’s side, and has earned two caps for his country Norway as well.
His gradual progress hasn’t gone unnoticed, and now a report claims that Dortmund are considering making a move for the youngster in the summer.
The German giants have already made contact with Celtic over a summer move, but the report doesn’t state clearly whether Celtic would be willing to sell at all.
In case they do, the Bhoys could land a huge profit. Celtic would be demanding a high transfer fee for the player, but in all probability they won’t sell him in the summer.