The 21-year-old was on target in Reykjavik to give Ronny Deila's side an important away goal as they set their sights on the group stages.
McGregor netted his first senior goal for the Scottish champions with seven minutes remaining and, after a fruitful loan spell at Notts County last season, he is keen to force his way into Deila's plans.
"I feel ready for this," he is quoted as saying in the Daily Record. "Going on loan to Notts County in League One was a big help to me.
"I feel like I have come back a better, stronger player. I feel mentally ready for this challenge now.
"Obviously I'm delighted with the goal and I'll enjoy it but I know I need to keep working. Once I get back into training on Thursday I'll get the head down and keep striving to be better.
"Being at Celtic means the world to me and if I can be here for a long time I'll be delighted."
Deila was pleased to have come through his first competitive game with a victory, and praised the effort shown by his squad in Iceland.
"If it had been 0-0, I would have been happy as well because of the performance," he said. "But we deserved a goal, maybe a couple more.
"In the second half, we were good at getting up the tempo going forward, and there was a lot of movement.
"When we lost the ball, we got it straight back again. That's how we want it."
