In manager Ronny Deila’s first competitive game since taking over from Neil Lennon last month, the Norwegian sprang a surprise when he handed the 21-year-old midfielder his competitive debut in the second qualifying round first leg against KR Reykjavik in Iceland.
But the Scotland Under-21 player, who spent a productive spell on loan at Notts County last season and impressed in pre-season friendlies, was to prove the difference.
In a frustrating night for the Scottish champions, Kris Commons, Leigh Griffiths and substitute Teemu Pukki all hit woodwork before 21-year-old McGregor drilled a shot low past home goalkeeper Stefan Magnusson with seven minutes remaining to secure a 1-0 advantage for the return leg.
Now McGregor wants to keep his place.
He said: “I spent last season with Notts County in [English] League One and I feel I have come back a better player. I feel that I am mentally ready to make the challenge.
“When you come back here you don’t want to leave. Being at Celtic means the world to me so if I can be here for a long time I will be delighted.
“Once I come in on Thursday I will get my head down and get working and strive to be better every day.
“But to score in the Champions League for Celtic – I have been there since I was nine years old – was a dream come true.
“It was a little bit of relief with it being 0-0 but I was absolutely delighted. It was a big night for the club, to strive to get Champions League football again, and that might be the goal that takes us through to the next round, so I am absolutely delighted.”
On McGregor’s performance, Deila said: “I think he did well on his debut.
“He has big talent but I want him to be more direct, go forward more and link up more with the full-back, but that will come and I am very happy for him that he scored a goal.”