The 21-year-old is determined to bounce back, however.
Like the club as a whole, McGregor has gone off the boil a bit recently, although things are still looking good for Celtic overall.
And McGregor, who says he was previously playing the best football of his career, admits it was difficult to keep up his high standards.
“I have had a wee dip in form. I was playing really well, probably playing the best football of my career, and it is hard to sustain that," the 21-year-old is quoted as saying by the Scotsman.
“It is a good learning curve for me to try and get back to that level and stay on it. That is the key to sustaining a long career at Celtic.
“It was a great year for me in 2014. I came back from my loan spell at Notts County, got into the Celtic first team, scored in the Champions League, got a Scotland call-up and then signed a new five-year contract. So hopefully I can continue to progress in 2015.”