The 27-year-old was stretchered off during Saints' defeat by Hibs way back on August 18, almost exactly a year after sustaining a similar injury against Dundee United on his other knee.
Given the level of promise the young centre-back had shown in bridging the two-tier gap between the Irn-Bru Second Division and the SPL, to suffer such a severe injury not once, but twice, is almost incomprehensible.
Now the likeable young stopper, who watched on from the stand as Saints went down 2-0 at Parkhead on Saturday, believes the experience of already having come back from the injury has stood him in good stead as he hopes to return to action before the end of the campaign.
The Buddies ace said: "It is now three months after the operation so I am roughly half-way through the rehab process and hope to be back training with the lads by March.
"To have suffered the same injury two years on the bounce has been really tough to take, but I am a very positive person and there are aspects you can focus in on.
"The great thing is that it was not the same knee. If it had been I would have been really struggling as the whole kneecap would have needed rebuilt.
"But the other big positive is that I have been through the whole process before and know exactly where I am and what the timescales are and that stops you putting too much pressure on yourself.
"So, although early on it was really tough, I have been able to be a lot stronger and upbeat this time.
"Ultimately my target is to be back playing in a couple of games before the season is over.
"But first it is get back into training with the squad, then feature in reserve games and then hopefully get back into the first team.
"I have another year left on my current deal so there is no point rushing things this time around."
The Buddies star has no doubt whatsoever about the toughest part of his week.
McGregor said: "Without doubt that has got to be on a Saturday.
"I have tried to stay involved with the first-team squad and to make sure I come to all the games and support the lads, but it is just very hard to be sitting in the stand all the time and helpless.
"On Saturday I sat in the main stand at Parkhead thinking I have only ever played here once before and wondering if that would be my one and only shot at it.
"But then you put that out of your mind and just become even more determined.
"The main thing for me is where I am in my rehab process. Everything is going well and on schedule and as long as you stay focused on that then you stay positive.
"I have absolutely no doubt I will be back but what matters is that when I do get back that this time it is for good."