Erik Sviatchenko fell out of favour under Brendan Rodgers last season and he now has another challenger for his Celtic posiiton.
Celtic boss Brendan Rodgers has changed Kristoffer Ajer's position to centre-back.
Celtic's youngster is relishing the prospect of facing Rosenborg.
Should Brendan Rodgers promote the "outstanding" Celtic talent instead of signing a replacement for Dedryck Boyata?
19-year-old defensive duo Kristoffer Ajer and Jamie McCart will return to Celtic with their reputations enhanced - but who impressed Brendan Rodgers most?
Celtic's Kristoffer Ajer is very highly regarded by Brendan Rodgers.
Jozo Simunovic and Erik Sviatchenko have been linked with the Premier League - but Kristoffer Ajer's development means Celtic have a bright future.
Kristoffer Ajer joined Kilmarnock from Celtic in the January transfer window.
Celtic loanee started for Celtic against Rangers.
The teenager Celtic defender helped to keep Rangers at bay on Wednesday night.
Ajer has barely featured under Bhoys boss Brendan Rodgers and is set to leave Celtic Park in January. Could Leeds United, Queens Park Rangers or Barnsley be the defender's next stop?
Celtic clearly have plenty of exciting teenagers coming through the ranks currently.
The Norwegian teen was looking forward to working with the departing Celtic boss.