The 18-year-old agreed a four-year deal in February while playing for Start in Norway but did not arrive until June, by which time his fellow Norwegian Ronny Deila had been replaced as Hoops manager by Brendan Rodgers.
Ajer, who can play in defence or midfield, came off the bench in the first half to replace Erik Sviatchenko after the Danish stopper had sustained a head knock in a clash with the visiting goalkeeper Diego Benaglio.
After a nervy start in his home debut with Celtic a goal down to a deflected strike by Wolfsburg defender Paul Seguin, he settled down and, indeed, was awarded man of the match as strikes by Callum McGregor and substitute Ryan Christie gave Rodgers victory against the German outfit in his first home game as boss.
Sviatchenko should be back for the second leg of the Champions League second qualifier against part-time Lincoln Red Imps on Wednesday night, when the Scottish champions will look to recover from a 1-0 defeat.
Ajer is ready if called upon, although defence rather than midfield – an area where Rodgers joked about having 20 players from which to choose – could be his best bet. He said: “I came to Celtic to play and if he gives me the opportunity I am ready.
“There are a lot of midfielders and he knows that I can play there and he also wants me to develop as a centre-half. I think it is really good to be able to play more positions.
“The only thing I am working on is to develop and play games and if that means I have to play centre-half I will play centre-half.
“I was extremely stressed and went out without warming-up and I made some mistakes in the beginning which I am not proud of but, after a while, I performed well and it was a big experience hearing the fans.
“It is a big honour playing for Celtic and to get man of the match was brilliant.
“It [Lincoln] was a disappointing result for us but if we play like we did [on Saturday] we will beat Lincoln on Wednesday and this is our only focus.”
Ajer was the only Celtic player to reappear for the second half yesterday, Rodgers having made ten changes during the interval as he continues to assess his squad ahead of the supposedly more testing Champions League qualifiers which lie ahead – a process which he may feel is more necessary following that humiliating defeat in Gibraltar.
One of those replacements was error-prone defender Efe Ambrose, who had been at fault for Red Imps’ winning goal. Yesterday he was at least able to negotiate the last 45 minutes against the Bundesliga side which reached the quarter-finals of last season’s Champions League without further mishap.
In the end it was a morale-boosting win for Rodgers’ side, particularly after having fallen behind thanks to a slice of misfortune.
Wolfsburg’s opener after 11 minutes resulted from a drive by Seguin, which deflected off defender Eoghan O’Connell and entered the net with goalkeeper Craig Gordon wrong-footed.
Ten minutes later, Celtic were back on level terms through McGregor. Driving forward, he attempted to pass to Moussa Dembele but the ball rebounded back to him after striking a Wolfsburg defender, so the midfielder unleashed a curling shot which found the net from 25 yards.
Celtic’s winner came just after the hour when Christie was helped by a ricochet as he forced his way past two visiting defenders before striking a low, left-foot shot beyond the reach of substitute goalkeeper Koen Casteels.
The match died during the remaining period, although Christie had a chance to increase Celtic’s lead near the end but, on this occasion, Casteels was equal to his effort.